Bit string

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

/**
 *    author:  Atreus
 *    created: 18.01.2019
**/
#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int a[3];

int main(){
	ios_base::sync_with_stdio(false);
	string s;
	cin >> s;
	a[0] = 1;
	ll answer = 0;
	
	int par = 0;
	for (int i = 0; i < s.size(); i++){
		par ^= (s[i] == '1');
		answer += a[par];
		a[par] ++;
	}
	cout << answer << endl;
}

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