Bit string

input/code.cpp: In function 'int main()':
input/code.cpp:49:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i <= n.size(); i++)
                  ~~^~~~~~~~~~~
input/code.cpp:51:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int j = i + 1; j <= n.size(); j++)
                       ~~^~~~~~~~~~~

#include <iostream>
#include <vector>
#include <stack>
#include <unordered_set>
#include <numeric>
#include <iterator>
#include <unordered_map>
#include <array>
#include <map>
#include <cstring>
#include <iomanip>
#include <string>
#include <algorithm>
#include <cmath>
#include <ctgmath>
#include <set>
#include <queue>
#include <fstream>
#include <ostream>
#include <list>
#include <string>
using namespace std;

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	string n;
	cin >> n;

	vector<int> pref;

	pref.push_back(0);
	for (auto i : n)
	{
		if (i == '1')
		{
			pref.push_back(pref.back() + 1);
		}
		else
		{
			pref.push_back(pref.back());
		}
	}

	int cnt = 0;
	for (int i = 0; i <= n.size(); i++)
	{
		for (int j = i + 1; j <= n.size(); j++)
		{
			if ((pref[j] - pref[i]) % 2 == 0)
			{
				cnt++;
			}
		}

	}
	cout << cnt << "\n";
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 1

Verdict: ACCEPTED

Test 7

Group: 1

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 16

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 17

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 18

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 19

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 20

Group: 3

Verdict: ACCEPTED

Test 21

Group: 3

Verdict: ACCEPTED