Assisting with 868A-Bark To Unlock

Problem - 868A - Codeforces

Error type: Wrong answer
Incorect case: Unsure
Extreme case: works

test 1:
yo
1
oy
Expected: “YES” works

test 2:
yo
100
aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa oy
Expected: "YES"works

test 3:
yo
1
ha
Expected: "NO"works

These test cases does work when run on the custom test case

#include<bits/stdc++.h>
using namespace std;

int main()
{
	string p; cin >> p;
	int n; cin >> n;
	vector<string> slist;
	while(n--)
	{
		string s; cin >> s;
		slist.push_back(s);
	}
	int len = slist.size();
	string substr = "";
	// the first 'pointer'
	for (int i = 0; i<len; i++)
	{
		// second 'pointer'
		for (int j = 0; j<len; j++){
			substr = string(1, slist[i][1]) + string(1, slist[j][0]);
			if (substr == p) {cout << "YES"; return 0;}
			substr = string(1, slist[j][1]) + string(1, slist[i][0]);
			if (substr == p) {cout << "YES"; return 0;}
		}
	}
	cout << "NO";
}

time complexity: 2 nested forloops; O(n^2)
there is maximum 100 elements; so 100^2 = 10,000 operations max
10^8 operations per sec, and we are given 2 seconds, so that is more than enough

My own test case runs fine in the custom test case: