Hello, Codeforces!↵
↵
In this series of articles, I would like to tell you about tips'n'tricks I use in C++ sources. Some of them require a strong C++ background, some not, but all of them are aimed to reduce the time you spend on basic things like reading input/debugging/etc, so it might be useful for your next template.↵
↵
This part is dedicated to some basic tips (and probably should've been the first part but it's not ¯\\_(ツ)_/¯).↵
↵
<spoiler summary="TL;DR">↵
Full code:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
using i64 = int64_t;↵
using f80 = long double;↵
↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
↵
template <class T> auto &operator>>(istream &is, vector<T> &xs)↵
{ for (auto &x : xs) is >> x; return is; }↵
↵
namespace io {↵
template <class ...As> auto &read(As &...as) { return (cin >> ... >> as); }↵
template <class ...As> auto &log(const As &...as) { return ((cerr << " " << as), ...); }↵
} // namespace io↵
↵
#define ALL(xs) begin(xs), end(xs)↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
} ↵
#define READ(...) __VA_ARGS__; io::read(__VA_ARGS__)↵
#define READ_CTOR(name, ...) name(__VA_ARGS__); io::read(name)↵
↵
#ifndef ONLINE_JUDGE↵
int recursion_depth = 0;↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
# define LOG(...) cerr << string(recursion_depth, '\t') \↵
<< "[ "#__VA_ARGS__" ] ="; \↵
io::log(__VA_ARGS__) << '\n'↵
# define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
#else↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
# define dbg(...) (__VA_ARGS__)↵
#endif↵
↵
auto main() -> int {↵
// write code here↵
}↵
↵
namespace {↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
} // namespace↵
↵
~~~~↵
↵
</spoiler>↵
↵
# `bits/stdc++.h`↵
↵
Just add this header to your source file and you won't have to add any other STL headers. Probably the only reason why you still haven't done it (if you haven't) is that it might not work on your machine: that happens because `bits/stdc++.h` is a feature of GCC, not the entire cpp standard. However, there're a few ways to work around it.↵
↵
## How to fix `bits/stdc++.h` if it's not working↵
↵
###Content↵
↵
Well, before we start putting `stdc++.h` to the proper location, there's one thing to determine: content to put in it. You either can determine what default headers you might need or just google "GCC bits/stdc++.h source" and copy/paste it [if you've decided to do so, you might need to remove some gcc-specific headers: just try to compile it and remove one by one non-compiling includes].↵
↵
###Option 1: Add it to default location↵
↵
Well, the easiest one is to find one of the include paths, like `/usr/local/include` (might add to `/usr/include`, but it's a system directory, do it at your own risk) on Mac, or [somewhere else for Windows](https://stackoverflow.com/questions/335408/where-does-visual-studio-look-for-c-header-files). All you need to do after this is to create folder `bits` and file `stdc++.h` inside it.↵
↵
###Option 2: Add to user-defined header search paths↵
↵
If you compile/run you code manually, there's the option of adding proper location as compiler flag `isystem` directly:↵
↵
~~~~↵
$ g++ -std=c++2077 a.cpp -o run_a -isystem /path/to/your/custom/includes↵
~~~~↵
↵
Note that inside the folder `/path/to/your/custom/includes` must be the folder `bits` with file `stdc++.h`.↵
↵
###Option 3: Add to you build system↵
↵
If you're using CMake based build system (which CLion is), then you could edit your `CMakeLists.txt` directly: ↵
↵
~~~↵
include_subdirectory(/path/to/your/custom/includes)↵
~~~↵
↵
# Typealiases↵
↵
In C++ there are a lot of strange things that came from ancient times, like `signed long long int` constructions. However, if you don't like such long type names, you could write `using NewType = ExistingType` or `typedef ExistingType NewType`. ↵
↵
A lot of programmers here, on CodeForces, use `ll` instead of `long long` and a bit less use `ld` instead of `long double`. Since C++11, we have `int64_t`, which is like `long long` but not that long. I could also suggest using the following (inspired by Rust):↵
↵
~~~~~↵
using i64 = int64_t;↵
using f80 = long double;↵
~~~~~↵
↵
`using` has an advantage over `typedef`: it supports templates, so you could shorten annoyingly long type names such as `vector` or `unordered_set(map)`:↵
↵
~~~~~↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
~~~~~↵
↵
By the way, if you've noticed that sometimes `map` works faster than `unordered_map` even on big inputs, it happens because of expensive and frequent rehashing hidden in `unordered_set(map)`. To work around it, I suggest calling `um.reserve(4 * MAX_ELEMENTS_EXPECTED)`. It will work much faster. You can also read [this article](https://codeforces.me/blog/entry/21853) to learn more about `unordered_map`.↵
↵
# Prewritten library code↵
↵
According to CodeForces' official rules, you might use some prewritten code. When it comes to some library-like code for things like fft, flows, or smth else you can find it annoying to search over your sources to copy/paste once you need it. One of the ways is to put all functionality you might need to separate files like `z.hpp` and simply include it [keep in mind the section about modifying header search paths].↵
↵
If you don't use the include, just remove it before submission, and if you need it, you can simply jump to definition (most of IDEs can do it using ctrl + click to source and copy/paste content before submitting. For example with [this file](https://github.com/dendi239/algorithms-data-structures/blob/master/algebra/z.hpp) you could write smth like:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
#include <z.hpp>↵
↵
using namespace std;↵
↵
constexpr int mod = 1000 * 1000 * 1000 + 7;↵
using Mint = Z<mod>;↵
↵
template <class T>↵
T bin_pow(T base, int64_t exponent) {↵
if (exponent == 0) return T(1);↵
if (exponent % 2 == 1)↵
return base * bin_pow(base * base, exponent / 2);↵
return bin_pow(base * base, exponent / 2);↵
}↵
↵
int main() {↵
Mint a, b;↵
cin >> a >> b;↵
↵
// note that the following addition is performed by modulo↵
cout << a + b << '\n';↵
↵
// note that because of the type of `a` bin_pow uses modular arithmetics↵
cout << bin_pow(a, b) << '\n';↵
}↵
~~~~↵
↵
Don't forget to copy/paste the actual source (if you're using it) to your file before submitting: there's no `z.hpp` accessible by codeforces's compiler. It may be enhanced by custom script doing it instead of you, but there's no such script yet ¯\\_(ツ)_/¯.↵
↵
# `stdin`, `stdout`, `stderr`↵
↵
Your program is using at least three streams to communicate with OS: `stdin` for input, `stdout` for output, and `stderr` for errors. Moreover, by default, there's sync for `cin` and `cout` which may slow down your solution on huge inputs. You could discover more [here](https://codeforces.me/blog/entry/5217?locale=en). If you don't like `ios::sync_with_stdio(false); cin.tie(nullptr);` appearing in `main` every time, you could use the following trick: if you need some side effects to happen even before `main` starts, you can do it when global variables instantiate:↵
↵
~~~~↵
int main() {↵
// some code↵
}↵
↵
// empty namespace to not conflict with any other possible names↵
namespace {↵
↵
// global variable is assigned to the result of calling the newly created lambda function.↵
// since your variable cannot be void, put `int` as a result:↵
auto fast_io = [] {↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
↵
return 0;↵
}();↵
↵
} // namespace↵
~~~~↵
↵
Since any checker/grader reads only `stdout`, I strongly recommend using `stderr` for debug information (`cerr` instead of `cout`) — that way once you find a bug and solve it, you won't need to remove all the debugging stuff before submitting. However, if you output to `stderr` a lot, it can affect the performance.↵
↵
## Interactive, custom files and other↵
↵
Sometimes you don't need `cin.tie` for interactive problems or debugging in your IDE. Moreover, sometimes you need to work with custom files. To resolve it, I can suggest using defines `INTERACTIVE` and `FILES`:↵
↵
~~~~↵
// example of usage, don't use both in real life↵
#define INTERACTIVE↵
#define FILES "k3"↵
↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
~~~~↵
↵
# Use some tooling↵
↵
Since you're writing some code and test it against a few test cases it may be annoying to write all of them on your own every time you run the program. To get rid of copypasting them from a webpage, or trying to copy with spaces from pdf, you could've put it into files at once and get input from these files. There's an amazing [tool](https://codeforces.me/blog/entry/66552) from [user:xalanq,2020-06-29] that does it for you. It ignores all your debug output while checking, but still prints it above the testing verdicts. Take a look at [this submission](https://codeforces.me/contest/1367/submission/85413433):↵
↵
~~~~↵
➜ b cf test ↵
g++ -std=c++17 b.cpp -o b.exe -O2 -DLOCAL -DDEBUG↵
[ n ] = 4↵
[ n ] = 3↵
[ n ] = 1↵
[ n ] = 7↵
Passed #1 ... 0.001s 0B↵
[ n ] = 4↵
[ n ] = 3↵
[ n ] = 1↵
[ n ] = 7↵
Passed #2 ... 0.001s 0B↵
rm b.exe↵
➜ b cf submit↵
Submit CONTEST 1367, problem b↵
Current user: dendi239↵
Submitted↵
#: 85413433↵
when: 2020-06-29 03:31↵
prob: B - Even Array↵
lang: GNU C++17↵
status: Accepted ↵
time: 61 ms↵
memory: 3.71 MB↵
~~~~↵
↵
# Run debug code only in debug mode↵
↵
You may need to run some extra code for debugging purposes only. For example, printing a graph, performing additional checks, or comparing with the naive solution. It may affect the resulting performance and move you from the AC zone to the TL one.↵
↵
There's the straightforward solution: use `#ifdef` preprocessor directive: ↵
↵
~~~~↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
#ifdef DEBUG↵
cerr << "a = " << a << " b = " << b << '\n'↵
#endif // DEBUG↵
cout << a + b << '\n';↵
~~~~↵
↵
To run this code in debug mode, you need to pass `-DDEBUG` or `-D DEBUG` option to your compiler. If you don't know how to do it, or simply don't wanna to do it, codeforces [defines](https://codeforces.me/blog/entry/79) `ONLINE_JUDGE` for you:↵
↵
~~~~↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
#ifndef ONLINE_JUDGE↵
cerr << "a = " << a << " b = " << b << '\n'↵
#endif // ONLINE_JUDGE↵
cout << a + b << '\n';↵
~~~~↵
↵
Plenty of code just to output two variables, isn't it? Let's solve two problems:↵
↵
* print all variables given to function (macro)↵
* write code (block, or just function) that runs in debug mode and doesn't evaluate arguments in release mode↵
↵
## Printing all variables↵
↵
Ok, let's provide macro `LOG(x, y, z)` that works like `cerr << "x = " << x << " y = " << y << " z = " << z << "\n"`, but works with plenty of arguments. Since we can't take `x` as string from function argument, let's start from simple scratch:↵
↵
~~~~↵
#define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
~~~~↵
↵
Where `log` function prints all arguments given to it. You could implement it the way I mentioned in [my previous article](https://codeforces.me/blog/entry/79066): ↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) {↵
return ((cerr << " " << as), ...) << '\n';↵
}↵
~~~~↵
↵
Let's put it all together:↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) {↵
return ((cerr << " " << as), ...) << '\n';↵
}↵
↵
#define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
↵
LOG(a, b, a + b);↵
// prints: [ a, b, a + b ] = 2 2 4↵
↵
cout << a + b << '\n';↵
}↵
~~~~↵
↵
Well, there are plenty of things you could've improved, as mentioned in [this discussion](https://codeforces.me/blog/entry/15643?#comment-205812). However, it still doesn't work fine for things with a comma in subexpressions like:↵
↵
~~~~↵
LOG(a, b, some_func(a, b))↵
~~~~↵
↵
## Running code in debug mode only↵
↵
How to run code in debug and don't evaluate arguments in release mode? Well, here's a trick you might have seen [here](https://codeforces.me/blog/entry/64218) involving `if`:↵
↵
~~~~↵
#ifndef DEBUG↵
↵
#define CERR if (false) cerr↵
↵
#endif↵
↵
// somewhere in code↵
↵
CERR << "a = " << a << '\n';↵
↵
// expands to↵
↵
if (false) cerr << << "a = " << a << '\n';↵
~~~~↵
↵
But there's bug here:↵
↵
~~~~↵
if (a == 0)↵
CERR << "b = " << b << '\n';↵
else {↵
CERR << "c = " << c << '\n';↵
// dance like no one's watching↵
// with a != 0↵
}↵
↵
// expands to↵
↵
if (a == 0)↵
if (false)↵
cerr << "b = " << b << '\n';↵
else {↵
if (false)↵
cerr << "c = " << c << '\n';↵
// a is still zero here :(↵
}↵
~~~~↵
↵
Well, there's an alternative with `while (false)` which doesn't have such bugs. But what to do instead of `while (false)` to run any code? We may try to put nothing [don't know if there's bug], but I'd prefer a one time running `for`. Let's put it all together:↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) ↵
{ return ((cerr << " " << as), ...) << '\n'; }↵
↵
#ifdef DEBUG↵
# define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
#else // DEBUG↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
#endif // DEBUG↵
↵
int main() {↵
int n, m;↵
cin >> n >> m;↵
↵
LOG(n, m);↵
↵
vector<vector<int>> g(n);↵
for (int e = 0; e < m; ++e) {↵
int u, v;↵
cin >> u >> v;↵
↵
g[--u].push_back(--v);↵
g[v].push_back(u);↵
}↵
↵
RUN {↵
for (int u = 0; u < n; ++i) {↵
cerr << u << ":";↵
for (int v : g[u]) ↵
cerr << " " << v;↵
cerr << "\n";↵
}↵
}↵
}↵
~~~~↵
↵
# `auto`↵
↵
There's the keyword to replace all the boring types you don't need to write explicitly:↵
↵
~~~~↵
for (auto it = xs.begin(); it != xs.end(); ++it)↵
for (auto foo : foos)↵
~~~~↵
↵
But there's a hidden problem: unnecessary copying: ↵
↵
~~~~↵
for (auto row : table) {↵
// here row has a type vector<Cell> ↵
// and it will be copied even if you don't modify it↵
}↵
~~~~↵
↵
To avoid it, you could've used:↵
↵
~~~~↵
for (auto &row : table)↵
~~~~↵
↵
But, it might be a temporary object, that's kind of annoying. To resolve it, you could've used universal reference everywhere:↵
↵
~~~~↵
// works just fine: no copies, ↵
// reference if regular object↵
// value if temporary one↵
for (auto &&row : table)↵
~~~~↵
↵
Ok, where to use it?↵
↵
## Predicates↵
↵
If you're using lambdas, you might still not know about [generic lambdas](https://en.cppreference.com/w/cpp/language/lambda), let me show the use case:↵
↵
~~~~↵
vector<pair<int, int>> some_events = ...;↵
sort(some_events.begin(), some_events.end(), [&](auto &&lhs, auto &&rhs) {↵
// compare two pair<int, int> here↵
});↵
~~~~↵
↵
You might have noticed that you often write code like `return foo(lhs) < foo(rhs);`. Here's the way to get rid of it: ↵
↵
~~~~↵
#define BY_FUNC(func) [&](auto &&lhs, auto &&rhs) { \↵
return func(lhs) < func(rhs); \↵
}↵
↵
sort(some_events.begin(), some_events.end(), BY_FUNC(some_func));↵
~~~~↵
↵
Much better (you can also come up with a shorter name for macro), but if you want to only compare by `.second`, it's not suitable (you'll still have to define `some_func` which takes a few extra lines) :(. However, we could generate all necessary code on our own (thanks to [user:viskonsin,2020-06-27] for pitching me this idea):↵
↵
~~~~↵
#define ALL(xs) begin(xs), end(xs)↵
↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
}↵
↵
sort(ALL(pairs), BY(x.second));↵
↵
// expands to:↵
↵
sort(pairs.begin(), pairs.end(), [&](auto &&lhs, auto &&rhs) {↵
auto predicate = [&](auto &&x) {↵
return x.second;↵
};↵
return predicate(lhs) < predicate(rhs);↵
});↵
↵
// such plenty of code out of one short macro!↵
~~~~↵
↵
## `dbg` macro↵
↵
Thanks to [user:ramchandra,2020-06-29] for his amazing `dbg` [macro](https://codeforces.me/blog/entry/79024), really nice job. There's also [the `dbg!` macro in Rust](https://doc.rust-lang.org/beta/std/macro.dbg.html). Let's develop the same behavior: `dbg(expr)` works as a simple `expr` in release mode and additionally prints it in debug mode. Well, the implementation for release mode is pretty straightforward:↵
↵
~~~~↵
#define dbg(...) (__VA_ARGS__)↵
~~~~↵
↵
And what about the debug one? I'd like to work with any kind of references here, to write smth like: ↵
↵
~~~~↵
auto it = dbg(order).find(dbg(x + 1));↵
~~~~↵
↵
Okay, it must be a result of expression with necessary debug output. Let's use a simple lambda on the fly (note that `forward` is used since we need to keep lvalue if it was passed and fallback to moving value if not: for `dbg(i + j)` we don't need to return a reference to local object):↵
↵
~~~~↵
int recursion_depth = 0;↵
#define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
~~~~↵
↵
# Conclusion↵
↵
You might have noticed that there's a lot of complicated things involved. It took me way more than 21 days to come up with all of these tips'n'tricks. Some of them contained bugs in the first version, others not. However, anytime you use macros it's unclear what they expand to and pretty easy to make a mistake. Don't use any single macro you're not feeling ready to debug a bit if necessary. If you don't feel comfortable in understanding some of these macros, prefer not to use them.↵
↵
Here's a simple way to make a mistake when dealing with `READ` macro:↵
↵
~~~~~↵
// does not compile↵
for (int READ(t); t--;)↵
↵
// expands to↵
for (int t; io::read(t); t--;)↵
↵
// why there're three ";" inside for?↵
~~~~~↵
↵
It took over half an hour to come up with `dbg` macro that worked as I wanted it to. I tried a lot of things, even stack overflow didn't give me an answer, but months of exploring STL sources gave me a simple hint (actually it was a question: "what I need to use `std::forward` for?").↵
↵
There's plenty of code, isn't it? Note that it may be overcomplicating to use every single of macros: just choose which ones you like and add them to your template. However, you could add all of them:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
using i64 = int64_t;↵
using f80 = long double;↵
↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
↵
template <class T> auto &operator>>(istream &is, vector<T> &xs)↵
{ for (auto &x : xs) is >> x; return is; }↵
↵
namespace io {↵
template <class ...As> auto &read(As &...as) { return (cin >> ... >> as); }↵
template <class ...As> auto &log(const As &...as) { return ((cerr << " " << as), ...); }↵
} // namespace io↵
↵
#define ALL(xs) begin(xs), end(xs)↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
} ↵
#define READ(...) __VA_ARGS__; io::read(__VA_ARGS__)↵
#define READ_CTOR(name, ...) name(__VA_ARGS__); io::read(name)↵
↵
#ifndef ONLINE_JUDGE↵
int recursion_depth = 0;↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
# define LOG(...) cerr << string(recursion_depth, '\t') \↵
<< "[ "#__VA_ARGS__" ] ="; \↵
io::log(__VA_ARGS__) << '\n'↵
# define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
#else↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
# define dbg(...) (__VA_ARGS__)↵
#endif↵
↵
auto main() -> int {↵
// write code here↵
}↵
↵
namespace {↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
} // namespace↵
↵
~~~~↵
↵
# What's next?↵
↵
There're amazing articles from [user:Golovanov399,2020-06-27] [here](https://codeforces.me/blog/entry/74684), and from [user:Swift,2020-06-27] [here](https://codeforces.me/blog/entry/15643) — check them, they cover a lot of things (like `all(xs)` macro) I omitted. There's also [another my article](https://codeforces.me/blog/entry/79066) about reading and declaring variables all at once. And more will come, stay tuned!↵
↵
I would like to thank: ↵
↵
* [user:viskonsin,2020-06-27] for help with editing this article↵
* [user:Golovanov399,2020-06-27], [user:Swift,2020-06-27] and [user:ramchandra,2020-06-27] for their amazing articles↵
* [user:xalanq,2020-06-27] for wonderful [cf-tool](https://github.com/xalanq/cf-tool)↵
* You for reading this article!↵
↵
See ya!
↵
In this series of articles, I would like to tell you about tips'n'tricks I use in C++ sources. Some of them require a strong C++ background, some not, but all of them are aimed to reduce the time you spend on basic things like reading input/debugging/etc, so it might be useful for your next template.↵
↵
This part is dedicated to some basic tips (and probably should've been the first part but it's not ¯\\_(ツ)_/¯).↵
↵
<spoiler summary="TL;DR">↵
Full code:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
using i64 = int64_t;↵
using f80 = long double;↵
↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
↵
template <class T> auto &operator>>(istream &is, vector<T> &xs)↵
{ for (auto &x : xs) is >> x; return is; }↵
↵
namespace io {↵
template <class ...As> auto &read(As &...as) { return (cin >> ... >> as); }↵
template <class ...As> auto &log(const As &...as) { return ((cerr << " " << as), ...); }↵
} // namespace io↵
↵
#define ALL(xs) begin(xs), end(xs)↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
} ↵
#define READ(...) __VA_ARGS__; io::read(__VA_ARGS__)↵
#define READ_CTOR(name, ...) name(__VA_ARGS__); io::read(name)↵
↵
#ifndef ONLINE_JUDGE↵
int recursion_depth = 0;↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
# define LOG(...) cerr << string(recursion_depth, '\t') \↵
<< "[ "#__VA_ARGS__" ] ="; \↵
io::log(__VA_ARGS__) << '\n'↵
# define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
#else↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
# define dbg(...) (__VA_ARGS__)↵
#endif↵
↵
auto main() -> int {↵
// write code here↵
}↵
↵
namespace {↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
} // namespace↵
↵
~~~~↵
↵
</spoiler>↵
↵
# `bits/stdc++.h`↵
↵
Just add this header to your source file and you won't have to add any other STL headers. Probably the only reason why you still haven't done it (if you haven't) is that it might not work on your machine: that happens because `bits/stdc++.h` is a feature of GCC, not the entire cpp standard. However, there're a few ways to work around it.↵
↵
## How to fix `bits/stdc++.h` if it's not working↵
↵
###Content↵
↵
Well, before we start putting `stdc++.h` to the proper location, there's one thing to determine: content to put in it. You either can determine what default headers you might need or just google "GCC bits/stdc++.h source" and copy/paste it [if you've decided to do so, you might need to remove some gcc-specific headers: just try to compile it and remove one by one non-compiling includes].↵
↵
###Option 1: Add it to default location↵
↵
Well, the easiest one is to find one of the include paths, like `/usr/local/include` (might add to `/usr/include`, but it's a system directory, do it at your own risk) on Mac, or [somewhere else for Windows](https://stackoverflow.com/questions/335408/where-does-visual-studio-look-for-c-header-files). All you need to do after this is to create folder `bits` and file `stdc++.h` inside it.↵
↵
###Option 2: Add to user-defined header search paths↵
↵
If you compile/run you code manually, there's the option of adding proper location as compiler flag `isystem` directly:↵
↵
~~~~↵
$ g++ -std=c++2077 a.cpp -o run_a -isystem /path/to/your/custom/includes↵
~~~~↵
↵
Note that inside the folder `/path/to/your/custom/includes` must be the folder `bits` with file `stdc++.h`.↵
↵
###Option 3: Add to you build system↵
↵
If you're using CMake based build system (which CLion is), then you could edit your `CMakeLists.txt` directly: ↵
↵
~~~↵
include_subdirectory(/path/to/your/custom/includes)↵
~~~↵
↵
# Typealiases↵
↵
In C++ there are a lot of strange things that came from ancient times, like `signed long long int` constructions. However, if you don't like such long type names, you could write `using NewType = ExistingType` or `typedef ExistingType NewType`. ↵
↵
A lot of programmers here, on CodeForces, use `ll` instead of `long long` and a bit less use `ld` instead of `long double`. Since C++11, we have `int64_t`, which is like `long long` but not that long. I could also suggest using the following (inspired by Rust):↵
↵
~~~~~↵
using i64 = int64_t;↵
using f80 = long double;↵
~~~~~↵
↵
`using` has an advantage over `typedef`: it supports templates, so you could shorten annoyingly long type names such as `vector` or `unordered_set(map)`:↵
↵
~~~~~↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
~~~~~↵
↵
By the way, if you've noticed that sometimes `map` works faster than `unordered_map` even on big inputs, it happens because of expensive and frequent rehashing hidden in `unordered_set(map)`. To work around it, I suggest calling `um.reserve(4 * MAX_ELEMENTS_EXPECTED)`. It will work much faster. You can also read [this article](https://codeforces.me/blog/entry/21853) to learn more about `unordered_map`.↵
↵
# Prewritten library code↵
↵
According to CodeForces' official rules, you might use some prewritten code. When it comes to some library-like code for things like fft, flows, or smth else you can find it annoying to search over your sources to copy/paste once you need it. One of the ways is to put all functionality you might need to separate files like `z.hpp` and simply include it [keep in mind the section about modifying header search paths].↵
↵
If you don't use the include, just remove it before submission, and if you need it, you can simply jump to definition (most of IDEs can do it using ctrl + click to source and copy/paste content before submitting. For example with [this file](https://github.com/dendi239/algorithms-data-structures/blob/master/algebra/z.hpp) you could write smth like:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
#include <z.hpp>↵
↵
using namespace std;↵
↵
constexpr int mod = 1000 * 1000 * 1000 + 7;↵
using Mint = Z<mod>;↵
↵
template <class T>↵
T bin_pow(T base, int64_t exponent) {↵
if (exponent == 0) return T(1);↵
if (exponent % 2 == 1)↵
return base * bin_pow(base * base, exponent / 2);↵
return bin_pow(base * base, exponent / 2);↵
}↵
↵
int main() {↵
Mint a, b;↵
cin >> a >> b;↵
↵
// note that the following addition is performed by modulo↵
cout << a + b << '\n';↵
↵
// note that because of the type of `a` bin_pow uses modular arithmetics↵
cout << bin_pow(a, b) << '\n';↵
}↵
~~~~↵
↵
Don't forget to copy/paste the actual source (if you're using it) to your file before submitting: there's no `z.hpp` accessible by codeforces's compiler. It may be enhanced by custom script doing it instead of you, but there's no such script yet ¯\\_(ツ)_/¯.↵
↵
# `stdin`, `stdout`, `stderr`↵
↵
Your program is using at least three streams to communicate with OS: `stdin` for input, `stdout` for output, and `stderr` for errors. Moreover, by default, there's sync for `cin` and `cout` which may slow down your solution on huge inputs. You could discover more [here](https://codeforces.me/blog/entry/5217?locale=en). If you don't like `ios::sync_with_stdio(false); cin.tie(nullptr);` appearing in `main` every time, you could use the following trick: if you need some side effects to happen even before `main` starts, you can do it when global variables instantiate:↵
↵
~~~~↵
int main() {↵
// some code↵
}↵
↵
// empty namespace to not conflict with any other possible names↵
namespace {↵
↵
// global variable is assigned to the result of calling the newly created lambda function.↵
// since your variable cannot be void, put `int` as a result:↵
auto fast_io = [] {↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
↵
return 0;↵
}();↵
↵
} // namespace↵
~~~~↵
↵
Since any checker/grader reads only `stdout`, I strongly recommend using `stderr` for debug information (`cerr` instead of `cout`) — that way once you find a bug and solve it, you won't need to remove all the debugging stuff before submitting. However, if you output to `stderr` a lot, it can affect the performance.↵
↵
## Interactive, custom files and other↵
↵
Sometimes you don't need `cin.tie` for interactive problems or debugging in your IDE. Moreover, sometimes you need to work with custom files. To resolve it, I can suggest using defines `INTERACTIVE` and `FILES`:↵
↵
~~~~↵
// example of usage, don't use both in real life↵
#define INTERACTIVE↵
#define FILES "k3"↵
↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
~~~~↵
↵
# Use some tooling↵
↵
Since you're writing some code and test it against a few test cases it may be annoying to write all of them on your own every time you run the program. To get rid of copypasting them from a webpage, or trying to copy with spaces from pdf, you could've put it into files at once and get input from these files. There's an amazing [tool](https://codeforces.me/blog/entry/66552) from [user:xalanq,2020-06-29] that does it for you. It ignores all your debug output while checking, but still prints it above the testing verdicts. Take a look at [this submission](https://codeforces.me/contest/1367/submission/85413433):↵
↵
~~~~↵
➜ b cf test ↵
g++ -std=c++17 b.cpp -o b.exe -O2 -DLOCAL -DDEBUG↵
[ n ] = 4↵
[ n ] = 3↵
[ n ] = 1↵
[ n ] = 7↵
Passed #1 ... 0.001s 0B↵
[ n ] = 4↵
[ n ] = 3↵
[ n ] = 1↵
[ n ] = 7↵
Passed #2 ... 0.001s 0B↵
rm b.exe↵
➜ b cf submit↵
Submit CONTEST 1367, problem b↵
Current user: dendi239↵
Submitted↵
#: 85413433↵
when: 2020-06-29 03:31↵
prob: B - Even Array↵
lang: GNU C++17↵
status: Accepted ↵
time: 61 ms↵
memory: 3.71 MB↵
~~~~↵
↵
# Run debug code only in debug mode↵
↵
You may need to run some extra code for debugging purposes only. For example, printing a graph, performing additional checks, or comparing with the naive solution. It may affect the resulting performance and move you from the AC zone to the TL one.↵
↵
There's the straightforward solution: use `#ifdef` preprocessor directive: ↵
↵
~~~~↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
#ifdef DEBUG↵
cerr << "a = " << a << " b = " << b << '\n'↵
#endif // DEBUG↵
cout << a + b << '\n';↵
~~~~↵
↵
To run this code in debug mode, you need to pass `-DDEBUG` or `-D DEBUG` option to your compiler. If you don't know how to do it, or simply don't wanna to do it, codeforces [defines](https://codeforces.me/blog/entry/79) `ONLINE_JUDGE` for you:↵
↵
~~~~↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
#ifndef ONLINE_JUDGE↵
cerr << "a = " << a << " b = " << b << '\n'↵
#endif // ONLINE_JUDGE↵
cout << a + b << '\n';↵
~~~~↵
↵
Plenty of code just to output two variables, isn't it? Let's solve two problems:↵
↵
* print all variables given to function (macro)↵
* write code (block, or just function) that runs in debug mode and doesn't evaluate arguments in release mode↵
↵
## Printing all variables↵
↵
Ok, let's provide macro `LOG(x, y, z)` that works like `cerr << "x = " << x << " y = " << y << " z = " << z << "\n"`, but works with plenty of arguments. Since we can't take `x` as string from function argument, let's start from simple scratch:↵
↵
~~~~↵
#define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
~~~~↵
↵
Where `log` function prints all arguments given to it. You could implement it the way I mentioned in [my previous article](https://codeforces.me/blog/entry/79066): ↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) {↵
return ((cerr << " " << as), ...) << '\n';↵
}↵
~~~~↵
↵
Let's put it all together:↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) {↵
return ((cerr << " " << as), ...) << '\n';↵
}↵
↵
#define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
↵
int main() {↵
int a, b;↵
cin >> a >> b;↵
↵
LOG(a, b, a + b);↵
// prints: [ a, b, a + b ] = 2 2 4↵
↵
cout << a + b << '\n';↵
}↵
~~~~↵
↵
Well, there are plenty of things you could've improved, as mentioned in [this discussion](https://codeforces.me/blog/entry/15643?#comment-205812). However, it still doesn't work fine for things with a comma in subexpressions like:↵
↵
~~~~↵
LOG(a, b, some_func(a, b))↵
~~~~↵
↵
## Running code in debug mode only↵
↵
How to run code in debug and don't evaluate arguments in release mode? Well, here's a trick you might have seen [here](https://codeforces.me/blog/entry/64218) involving `if`:↵
↵
~~~~↵
#ifndef DEBUG↵
↵
#define CERR if (false) cerr↵
↵
#endif↵
↵
// somewhere in code↵
↵
CERR << "a = " << a << '\n';↵
↵
// expands to↵
↵
if (false) cerr << << "a = " << a << '\n';↵
~~~~↵
↵
But there's bug here:↵
↵
~~~~↵
if (a == 0)↵
CERR << "b = " << b << '\n';↵
else {↵
CERR << "c = " << c << '\n';↵
// dance like no one's watching↵
// with a != 0↵
}↵
↵
// expands to↵
↵
if (a == 0)↵
if (false)↵
cerr << "b = " << b << '\n';↵
else {↵
if (false)↵
cerr << "c = " << c << '\n';↵
// a is still zero here :(↵
}↵
~~~~↵
↵
Well, there's an alternative with `while (false)` which doesn't have such bugs. But what to do instead of `while (false)` to run any code? We may try to put nothing [don't know if there's bug], but I'd prefer a one time running `for`. Let's put it all together:↵
↵
~~~~↵
template <class ...Args>↵
auto &log(const Args &...args) ↵
{ return ((cerr << " " << as), ...) << '\n'; }↵
↵
#ifdef DEBUG↵
# define LOG(...) cerr << "[ "#__VA_ARGS__" ] = "; log(__VA_ARGS__) << '\n'↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
#else // DEBUG↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
#endif // DEBUG↵
↵
int main() {↵
int n, m;↵
cin >> n >> m;↵
↵
LOG(n, m);↵
↵
vector<vector<int>> g(n);↵
for (int e = 0; e < m; ++e) {↵
int u, v;↵
cin >> u >> v;↵
↵
g[--u].push_back(--v);↵
g[v].push_back(u);↵
}↵
↵
RUN {↵
for (int u = 0; u < n; ++i) {↵
cerr << u << ":";↵
for (int v : g[u]) ↵
cerr << " " << v;↵
cerr << "\n";↵
}↵
}↵
}↵
~~~~↵
↵
# `auto`↵
↵
There's the keyword to replace all the boring types you don't need to write explicitly:↵
↵
~~~~↵
for (auto it = xs.begin(); it != xs.end(); ++it)↵
for (auto foo : foos)↵
~~~~↵
↵
But there's a hidden problem: unnecessary copying: ↵
↵
~~~~↵
for (auto row : table) {↵
// here row has a type vector<Cell> ↵
// and it will be copied even if you don't modify it↵
}↵
~~~~↵
↵
To avoid it, you could've used:↵
↵
~~~~↵
for (auto &row : table)↵
~~~~↵
↵
But, it might be a temporary object, that's kind of annoying. To resolve it, you could've used universal reference everywhere:↵
↵
~~~~↵
// works just fine: no copies, ↵
// reference if regular object↵
// value if temporary one↵
for (auto &&row : table)↵
~~~~↵
↵
Ok, where to use it?↵
↵
## Predicates↵
↵
If you're using lambdas, you might still not know about [generic lambdas](https://en.cppreference.com/w/cpp/language/lambda), let me show the use case:↵
↵
~~~~↵
vector<pair<int, int>> some_events = ...;↵
sort(some_events.begin(), some_events.end(), [&](auto &&lhs, auto &&rhs) {↵
// compare two pair<int, int> here↵
});↵
~~~~↵
↵
You might have noticed that you often write code like `return foo(lhs) < foo(rhs);`. Here's the way to get rid of it: ↵
↵
~~~~↵
#define BY_FUNC(func) [&](auto &&lhs, auto &&rhs) { \↵
return func(lhs) < func(rhs); \↵
}↵
↵
sort(some_events.begin(), some_events.end(), BY_FUNC(some_func));↵
~~~~↵
↵
Much better (you can also come up with a shorter name for macro), but if you want to only compare by `.second`, it's not suitable (you'll still have to define `some_func` which takes a few extra lines) :(. However, we could generate all necessary code on our own (thanks to [user:viskonsin,2020-06-27] for pitching me this idea):↵
↵
~~~~↵
#define ALL(xs) begin(xs), end(xs)↵
↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
}↵
↵
sort(ALL(pairs), BY(x.second));↵
↵
// expands to:↵
↵
sort(pairs.begin(), pairs.end(), [&](auto &&lhs, auto &&rhs) {↵
auto predicate = [&](auto &&x) {↵
return x.second;↵
};↵
return predicate(lhs) < predicate(rhs);↵
});↵
↵
// such plenty of code out of one short macro!↵
~~~~↵
↵
## `dbg` macro↵
↵
Thanks to [user:ramchandra,2020-06-29] for his amazing `dbg` [macro](https://codeforces.me/blog/entry/79024), really nice job. There's also [the `dbg!` macro in Rust](https://doc.rust-lang.org/beta/std/macro.dbg.html). Let's develop the same behavior: `dbg(expr)` works as a simple `expr` in release mode and additionally prints it in debug mode. Well, the implementation for release mode is pretty straightforward:↵
↵
~~~~↵
#define dbg(...) (__VA_ARGS__)↵
~~~~↵
↵
And what about the debug one? I'd like to work with any kind of references here, to write smth like: ↵
↵
~~~~↵
auto it = dbg(order).find(dbg(x + 1));↵
~~~~↵
↵
Okay, it must be a result of expression with necessary debug output. Let's use a simple lambda on the fly (note that `forward` is used since we need to keep lvalue if it was passed and fallback to moving value if not: for `dbg(i + j)` we don't need to return a reference to local object):↵
↵
~~~~↵
int recursion_depth = 0;↵
#define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
~~~~↵
↵
# Conclusion↵
↵
You might have noticed that there's a lot of complicated things involved. It took me way more than 21 days to come up with all of these tips'n'tricks. Some of them contained bugs in the first version, others not. However, anytime you use macros it's unclear what they expand to and pretty easy to make a mistake. Don't use any single macro you're not feeling ready to debug a bit if necessary. If you don't feel comfortable in understanding some of these macros, prefer not to use them.↵
↵
Here's a simple way to make a mistake when dealing with `READ` macro:↵
↵
~~~~~↵
// does not compile↵
for (int READ(t); t--;)↵
↵
// expands to↵
for (int t; io::read(t); t--;)↵
↵
// why there're three ";" inside for?↵
~~~~~↵
↵
It took over half an hour to come up with `dbg` macro that worked as I wanted it to. I tried a lot of things, even stack overflow didn't give me an answer, but months of exploring STL sources gave me a simple hint (actually it was a question: "what I need to use `std::forward` for?").↵
↵
There's plenty of code, isn't it? Note that it may be overcomplicating to use every single of macros: just choose which ones you like and add them to your template. However, you could add all of them:↵
↵
~~~~↵
#include <bits/stdc++.h>↵
↵
using namespace std;↵
↵
using i64 = int64_t;↵
using f80 = long double;↵
↵
using Str = string;↵
template <class T> using Vec = vector<T>;↵
template <class K, class V> using UM = unordered_map<K, V>;↵
↵
template <class T> auto &operator>>(istream &is, vector<T> &xs)↵
{ for (auto &x : xs) is >> x; return is; }↵
↵
namespace io {↵
template <class ...As> auto &read(As &...as) { return (cin >> ... >> as); }↵
template <class ...As> auto &log(const As &...as) { return ((cerr << " " << as), ...); }↵
} // namespace io↵
↵
#define ALL(xs) begin(xs), end(xs)↵
#define BY(...) [&](auto &&lhs, auto &&rhs) { \↵
auto predicate = [&](auto &&x) { \↵
return __VA_ARGS__; \↵
}; \↵
return predicate(lhs) < predicate(rhs); \↵
} ↵
#define READ(...) __VA_ARGS__; io::read(__VA_ARGS__)↵
#define READ_CTOR(name, ...) name(__VA_ARGS__); io::read(name)↵
↵
#ifndef ONLINE_JUDGE↵
int recursion_depth = 0;↵
# define RUN for (bool _flag = true; _flag; _flag = !_flag)↵
# define LOG(...) cerr << string(recursion_depth, '\t') \↵
<< "[ "#__VA_ARGS__" ] ="; \↵
io::log(__VA_ARGS__) << '\n'↵
# define dbg(...) [&]() -> auto && { \↵
++recursion_depth; \↵
auto&& value = __VA_ARGS__; \↵
--recursion_depth; \↵
cerr << string(recursion_depth, '\t') \↵
<< #__VA_ARGS__" = " << value \↵
<< endl; \↵
return forward<decltype(value)>(value); \↵
}()↵
#else↵
# define LOG(...) while (false) cerr↵
# define RUN while (false)↵
# define dbg(...) (__VA_ARGS__)↵
#endif↵
↵
auto main() -> int {↵
// write code here↵
}↵
↵
namespace {↵
auto fast_io = [] {↵
#ifndef DEBUG↵
# ifndef INTERACTIVE↵
ios::sync_with_stdio(false);↵
cin.tie(nullptr);↵
# endif // INTERACTIVE↵
# ifdef FILES↵
freopen(FILES".in", "r", stdin);↵
freopen(FILES".out", "w", stdout);↵
# endif // FILES↵
#endif // DEBUG↵
return 0;↵
};↵
} // namespace↵
↵
~~~~↵
↵
# What's next?↵
↵
There're amazing articles from [user:Golovanov399,2020-06-27] [here](https://codeforces.me/blog/entry/74684), and from [user:Swift,2020-06-27] [here](https://codeforces.me/blog/entry/15643) — check them, they cover a lot of things (like `all(xs)` macro) I omitted. There's also [another my article](https://codeforces.me/blog/entry/79066) about reading and declaring variables all at once. And more will come, stay tuned!↵
↵
I would like to thank: ↵
↵
* [user:viskonsin,2020-06-27] for help with editing this article↵
* [user:Golovanov399,2020-06-27], [user:Swift,2020-06-27] and [user:ramchandra,2020-06-27] for their amazing articles↵
* [user:xalanq,2020-06-27] for wonderful [cf-tool](https://github.com/xalanq/cf-tool)↵
* You for reading this article!↵
↵
See ya!
