Bit string

/*input
01011
*/
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
int main()
{
	ios_base::sync_with_stdio(false);
	string s;
	cin >> s;
	ll k[2] = {1, 0};
	ll suma = 0;
	ll ans = 0;
	for (char x : s)
	{
		if (x == '1')
		{
			suma = (suma + 1) % 2;
		}
		ans += k[suma];
		k[suma]++;
	}
	cout << ans << "\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: 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