can i use "ios::sync_with_stdio(false)" with cin/cout instead of scanf/printf in c++ or it's Better to Use scanf/printf ?

А как в интерактивной задаче работают взломы?
UPD: нашел в тексте поста. Описывается в условии задачи.

Известно под каким номером будет интерактивная задача?

how would you test these kinds of problems on your local computer?

Here is another interactive problem to try from (2012-2013 ACM-ICPC, NEERC, Moscow Subregional Contest):

J. Just Another Disney Problem

You don't need "return 0;" for interactive problems?

Наконец-то, а несколько лет назад почему-то говорили, что нельзя, что это плохо, что никто не поймет, что непонятно как взломы делать, и т.д.

In hacks, how would the "output" of model/participant solution be shown?

For some problem like this or this it seems we can see the whole process (look at some submissions), but the example problem from this post just shows the hidden number and the number of queries.

It is very funny :D using binary search (the exact code of blog) with L = 1, R = 1e6+6 got wrong answer on test 6, but L = 1, R = 1e6 got Accepted!

L = 1, R = 1e6+6: submission L = 1, R = 1e6: submission

Here's another interactive problem. https://www.codechef.com/MAY16/problems/CHBLLS Anyone interested may take a look. My first interactive problem. I enjoyed the solution but didn't like that flushing part somehow :v Even if someone understands the logic, he has the chance to get a wrong verdict for the syntax.

Hello,
why such code could get TLE on test 2 while if I just change the reckoning of mid to be the same as in the blog it gets AC .
any help would be highly appreciated

int main() {
    int l = 1, r = 1e6+10;
    while(l < r){
        int mid = (l+r)>>1;
        printf("%d\n",mid); fflush(stdout);
        char s[10]; scanf("%s",s);
        if(s[0]=='<') r = mid-1;
        else l = mid;
    }
    printf("! %d\n",l); fflush(stdout);
    return 0;
}

My solution gets Idleness Limit Exceeded, even though I flush the buffer. Where do you think the problem is?

18300219

UPD: I've found the error! I should've printed one query per line.

hello,
any one could tell me why this code gets TLE on test 2 whilst the same code in the blog gets AC which just differs in reckoning of mid, while I make r equals to 1e6+1 to evade that .
any help would be highly appreciated

int main() {
    int l = 1, r = 1e6+1;
    while(l < r){
        int mid = (l+r)>>1;
        printf("%d\n",mid); fflush(stdout);
        char s[10]; scanf("%s",s);
        if(s[0]=='<') r = mid-1;
        else l = mid;
    }
    printf("! %d\n",l); fflush(stdout);
    return 0;
}

why in this round ? you could use it in the educational first

Getting Idleness limit exceeded on test 1 in the first given problem. Here is my code. How can I fix it?

An Educational Round on this type of Problems would be better to understand the Submit / Hacking System .

Mike don't get me wrong it sounds like this contest is gonna be brilliant but couldn't you post this earlier like a day or two earlier.

or you could have tried it with educational rounds first like Deathly_Hallows said.

Nevertheless I wish happy coding for everyone and high ratings good luck.

:)

В каком дивизионе будет интерактивная задача?

what will be the verdict for making more than 25 queries???!!

The example section looks a bit misleading: why ">=" / "<" are output instead of input? And I think it'd be better to arrange them chronologically, like this.

Why's that "r = mid - 1" and "l = mid" gets AC and "r = mid - 1" and "l = mid + 1" gets WA? Can someone explain it?

I recommend not to penalize errors on 1 test for the interactive problem as many people might get confused initially.

I guess Input and Output were mutually misplaced?

I need to Input '<=' and '>' and let computer to guess and Output the number?

All the problems will be "Interactive"? All 5 from today's contest?

[Deleted]

Would it be possible to hack an interactive problem?

All the problems will be interactive?

My first ever solved interactive problem on any oj codechef: MAY16 "Chef and Balls"

If you have a question

{

for (int i = 0; i < 100; i++)

{

    reread the blog;

    reread all comments;

    if you have found the answer

        goodbye;

}

ask your question in comments;

goodbye;

}

Doesn’t std::endl flush the output buffer in C++ and doesn’t std::cin flush it as well? I’m pretty much surprised that 18314320 fails while 18315037 gets accepted.

It's very important to specify whether the system actually "hides" a fixed integer before interaction starts or the interactor can change the number (or any other information, in general) during testing in a way consistent with previous answers. In the former case, some probabilistic solutions to some problems can pass. In the latter, they won't.

As far as I can see, the only place in the example problem which mentions it is "it's fine to guess — if you guess correctly".

Maybe there should be another status for protocol failure (e.g. query limit exceeded)? Even Runtime Error would be much better than WA.

Можете исправить ошибку в решении на паскаль? Или хотя бы подсказать где она

uses dos;
var l,r,n:longint;
 c:char;
 begin
   l:=1;
   r:=1000000000;
   while l<r do
   begin
   writeln((r-l)div 2+l);   
    flush(output);
    readln(c);
    if c='<' then r:=(r-l)div 2+l else l:=l+(r-l)div 2;
    if r-l=1 then begin 
                    write('! ',l); 
                    flush(output);
                    break;
                  end;
  end;
end.

Please Help Me Out ..

I am trying to solve the Interactive Problem given in the above Link as there may be an Interactive Problem in today's Round . I have submitted a Code for practice several times. But Its showing WA at Test 1 . Don't know why .

Problem: http://codeforces.me/gym/101021/problem/A

Here is My code: http://pastebin.ubuntu.com/23172422/

It'd be very helpful if you please point me out the erroneous point of my Code .

Thanks in Advance .

Is writing fflush(stdout); at the end of main() necessary or redundant?

In Python 3, print() is a function and it has an optional parameter "flush" with a default value false. So you can just set it to true when needed to flush the output stream. print("blah blah", flush = True)

Any idea what this error means

wrong output format Unexpected end of file - token expected

submission

Even this works

cout.flush();

Can some one explain why this

int mid = (r+1+l)/2;  (work)
int mid = l+(r-l)/2;  (not work)

In the just concluded contest, I couldn't accept the input in python 2.

Problem: https://codeforces.me/contest/1011/problem/D

My simple solution:

n, m = map(int, raw_input().split())
print 1
raw_input()

The verdict: Idleness limit exceeded.

Any help is appreciated.

Why is this solution wrong?

/* _______ _______ _______ _______ _______ _______ ( ____ ( ____ ( )( ____ )( ____ ( ____ ) | ( \/| ( \/| () () || ( )|| ( \/| ( )| | (_____ | (__ | || || || (____)|| (__ | (____)| (_____ )| ) | |(_)| || _____)| ) | __) ) || ( | | | || ( | ( | (\ (
/_) || (__/| ) ( || ) | (____/| ) \ __ _______)(_______/|/ ||/ (_______/|/ __/

_______ _________ ______ _______ _ _________ _______ ( ____ __ /( __ \ ( ____ ( \ __ /( ____ \ | ( \/ ) ( | ( \ )| ( \/| ( ) ( | ( \/ | ( | | | | ) || ( | | | | | (_____ | ) | | | | | || ) | | | | (_ ) | ( | | | | ) || ( | | | | ) | | ) ) (| (__/ )| (____/| (____/___) (___/____) | |/ _______/(______/ (_______/(_______/_______/_______)

*/

include <bits/stdc++.h>

using namespace std;

define ll long long

define N 100005

define ld long double

define M 1000000007

define dd double

define rep(i,a,n) for(int i = a; i < n; i++)

define sep(i,n,b) for(int i=n-1;i>=b;i--)

define pb push_back

define mp make_pair

define Mll map<ll,ll>

define clr(x) x.clear()

define sz(x) ((int)(x).size())

define F first

define S second

int main() { int repeat=25; string tans; int start=0; int end=1000000; int mid=(start+end)/2; cout << mid << "\n"; cin >> tans; map<int,int> v; while(repeat--){ if(tans=="<"){ v[mid]=10; if(v[mid]==10 && v[mid+1]==11){ cout << "! " << mid+1 << endl; fflush(stdout); return 0; } start=mid; mid=(start+end)/2; cout << mid << "\n"; fflush(stdout); cin >> tans; } else if(tans==">="){ v[mid]=11; if(v[mid]==11 && v[mid-1]==10){ cout << "! " << mid << endl; fflush(stdout); return 0; } end=mid; mid=(start+end)/2; cout << mid << "\n"; fflush(stdout); cin >> tans; } } return 0; }

// >=

Why is this solution wrong?

http://codeforces.me/gym/101021/submission/47026197

Can someone explain why "L" is printed and not MID? And also when to print L , MID and R in binary search problems?

Who wants to add new Interactive problen tag?

Can I use "system("cls");" instead of "fflush(stdout);" in C++?

80301018 I am getting WA on test 6. I don't know why. can anyone help?

If i solved one of them would it be worth for rating?

Why do I still get the Idleness error despite of using flush after output (I have tried both flush after each output and just after the last output).

Can I use endl to achieve the effect of fflush(stdout)?

Sometimes on the Codeforces Rounds interactive problems will use. In this case the fromat of tests for hacks will described in the statements of the problems.

It should be format, not fromat, thought this isn't a big problem lol.

I cout<<endl and still get idleness limit exceeded. Why?

Example solution in JavaScript V8.

var left = 1
var right = 1000001
while (left + 1 < right) {
   var mid = parseInt((left + right) / 2)
   print(mid)
   var msg = readline()
   if (msg == "<") {
      right = mid
   } else {
      left = mid
   }
}
print("! " + left)

And also an example solution in Node.js. This version is a little trickier (due to the input feature) — it does not contain an explicit loop.

const readline = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});

var left = 1;
var right = 1000001;
var mid = parseInt((left + right) / 2);
console.log(mid);

readline.on('line', line => {
   if (line == "<") {
      right = mid;
   } else {
      left = mid;
   }
   if (left + 1 == right) {
      console.log("! " + left);
      readline.close();
   } else {
      mid = parseInt((left + right) / 2);
      console.log(mid);
   }
});

Curious as it is, my PyPy 3-64 solution got RTE when there was stdout.flush(): 274676159, but then after I removed stdout.flush() it got Accepted: 274676253.

if we will do it by linear search then it will take o(N) time which will give tle first time doing interactive question just asking for it so