Hello, CodeForces!

Information

I wrote a test generator on C++. It is very simple, it contains 2 functions: "generate a random number between $$$a$$$ and $$$b$$$, so that this random number is a multiple of $$$k$$$" (function: genint(a, b, k, add), where add is whether to "add" this number to the test) and "generate of a random string". There's something to be written here.

• Generates a string of random length between $$$a$$$ and $$$b$$$, so that it is a multiple of $$$k$$$.
• Consisting of the given characters. You can set characters in two ways: write the interval ("a-f", "x-z") or a individual character ("m", "o"). (function: genstr(a, b, k, pattern, add), where pattern is an array of given intervals or individual characters).

#include <bits/stdc++.h>
using namespace std;
#define int long long
string test = "";

int genint(int a, int b, int k, bool add) {
  if (a == b) {
    if (add) test += to_string(a);
    return a;
  }
  int ans = (rand() % (b / k - a / k) + (a / k + (a % k != 0))) * k;
  if (add) test += to_string(ans);
  return ans;
}

string genstr(int a, int b, int k, vector <string> p, bool add) {
  int l = genint(a, b, k, 0);
  vector <char> symbols;
  for (int i = 0; i < p.size(); i++) {
    if (p[i].size() == 1) {
      symbols.push_back(p[i][0]);
    } else {
      for (char j = p[i][0]; j <= p[i][2]; j++) {
        symbols.push_back(j);
      }
    }
  }
  string ans = "";
  for (int i = 0; i < l; i++) {
    ans += symbols[genint(0, symbols.size(), 1, 0)];
  }
  if (add) test += ans;
  return ans;
}

signed main() {
  srand(time(NULL));
  // generating test

  // ---------------
  freopen("test", "w", stdout);
  cout << test;
}

Usage

Here is a problem: You are given a string length of $$$n (n \le 10^5)$$$. You need to find the percentage of content of each character that is in the string (your answer will be considered correct if its absolute or relative error won't exceed $$$10^{-5}$$$). Example input and output:

Input
1
5
abcde
Output
a 20
b 20
c 20
d 20
e 20

Input
1
5
abcda
Output
a 40
b 20
c 20
d 20

You need to process $$$t$$$ testcases

For us, the competitors, this task is very simple, but for the authors it's necessary to write such tests, in which there will be both border and normal cases. Writing it by hand is a bad option. Especially since $$$n \le 10^5$$$.

With my generator you can make good tests in a few lines:

const int mintestcases = 5;
const int maxtestcases = 8;
const int minlength = 10;
const int maxlength = 20;
for (int i = 0; i < 5; i++) { // generates 5 tests
  string test = "";
  int t = genint(mintestcases, maxtestcases, 1, true);
  test += '\n';
  for (int j = 0; j < t; j++) {
    int n = genint(minlength, maxlength, 5, true);
    test += '\n';
    genstr(n, n, 1, {"a-z"}, true);
    test += '\n';
  }
}

Test 1

7
15
qghumeaylnlfdxf
10
rcvscxggbw
10
fnqduxwfnf
10
zvsrtkjpre
15
ggxrpnrvystmwcy
10
yycqpevike
15
fmznimkkasvwsre

Test 2

6
15
kycxfxtlsgypsfa
15
pooefxzbcoejuvp
15
aboygpoeylfpbnp
15
jvrvipyamyehwqn
10
rqpmxujjlo
10
vaowuxwhms

Test 3

6
10
bxcoksfzkv
10
txdknlyjyh
15
ixjswnkkufnuxxz
15
zbmnmgqooketlyh
15
koaugzqrcddiute
10
ojwayyzpvs

Test 4

5
10
psajlfvgub
15
aaovlzylntrkdcp
10
srtesjwhdi
15
cobzcnfwlqijtvd
10
vxhrcbldvg

Test 5

7
15
wgbusbmborxtlhc
10
mpxohgmgnk
10
ufdxotogbg
15
peyanfetcukepzs
15
kljugggekjdqzje
15
pevqgxiepjsrdzj
10
zujllchhbf

To make large tests you should increase values: mintestcases, maxtestcases, minlength, maxlength. For pretests you can take 1-2 tests of each "size".

You can generate strings consisting of uppercase letters: genstr(10, 20, 5, {"A-D"}, true), result: DCABACCCABBBBDBD.

You can also generate a string consisting of lowercase and uppercase letters: genstr(10, 20, 5, {"A-D", "a-d"}, true), result: DcaBaccCABBBBDBD.

Conclusion

This generator is also good for stress testing. Generating tests in a task is usually not very difficult. Also it can be used for hacks. You can generate a "maximal" test very easily.

Lucky rounds and high rating to all, bye!