Bit string

input/code.cpp: In function 'int main()':
input/code.cpp:20:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(ll i = 0; i < s.size(); i++)
                   ~~^~~~~~~~~~
input/code.cpp:41:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(ll i = 0; i < s.size(); i++)
                   ~~^~~~~~~~~~

#include <bits/stdc++.h>

using namespace std;

#define ll long long



int main()
{
    string s;

    cin >> s;

    vector<ll> n_1;

    ll ans = 0;


    for(ll i = 0; i < s.size(); i++)
    {
        if(i == 0)
        {
            if(s[0] == '0')
                n_1.push_back(0);
            else
                n_1.push_back(1);
        }

        else if(s[i] == '1')
            n_1.push_back(n_1[i - 1] + 1);

        else
            n_1.push_back(n_1[i - 1]);
    }

    ll e = 0;

    ll o = 0;

    for(ll i = 0; i < s.size(); i++)
    {
        if(n_1[i] % 2 == 0)
        {
            e++;
        }
        else
        {
            o++;
        }
    }

    ans += e;

    ans += (e - 1) * e / 2;

    ans += (o - 1) * o / 2;

    cout << ans;
    return 0;
}

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: ACCEPTED

Test 16

Group: 3

Verdict: ACCEPTED

Test 17

Group: 3

Verdict: ACCEPTED

Test 18

Group: 3

Verdict: ACCEPTED

Test 19

Group: 3

Verdict: ACCEPTED

Test 20

Group: 3

Verdict: ACCEPTED

Test 21

Group: 3

Verdict: ACCEPTED