In a recent contest: Codeforces Round 871 (Div. 4), I saw a Successful hacking attempt in the Hacks list. But I think this hacking may involve cheating.

Look at this hacked submission: 204925830

The source code of the defender contained a “landmine”, which means that for some corner case, the code wouldn’t be accepted.

Following is the source code. Note the corner case that would make the code wrong.

#include <algorithm>
#include <iostream>
#include <cstring>
#include <cstdio>
#include <vector>
#include <cmath>
#include <queue>
#include <stack>
#include <set>
#include <map>

using namespace std;

string s1,s2;
int t;

int main(){
	scanf("%d",&t);
	s1 = "codeforces";
	int ans;
	while(t --){
		cin >> s2;
		if(s2 == "xxxxxxxxxx"){ // Here! The corner case
			puts("-1"); // Wrong output
			return 0;
		}
		ans = 0;
		for(unsigned int i = 0 ; i < s1.size() ; ++i){
			if(s1[i] != s2[i])
				++ans;
		}
		printf("%d\n",ans);
	}
	return 0;
}

So, for the case xxxxxxxxxx, the code would definitely get a Wrong answer.

Then view the hacking test.