Bittijono

#include <iostream>

using namespace std;

bool t[505050];
int e[505050], o[505050];

int main() {
	string s;
	cin >> s;
	int n = s.size();
	for (int i = 0; i < n; i++) {
		t[i] = s[i] == '1';
	}
	o[0] = t[0];
	e[0] = !t[0];
	int c = e[0];
	for (int i = 1; i < n; i++) {
		if (t[i]) {
			e[i] = o[i-1];
			o[i] = e[i-1]+1;
		} else {
			e[i] = e[i-1]+1;
			o[i] = o[i-1];
		}
		c += e[i];
	}
	cout << c << 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: WRONG ANSWER

Test 16

Group: 3

Verdict: WRONG ANSWER

Test 17

Group: 3

Verdict: WRONG ANSWER

Test 18

Group: 3

Verdict: WRONG ANSWER

Test 19

Group: 3

Verdict: WRONG ANSWER

Test 20

Group: 3

Verdict: ACCEPTED

Test 21

Group: 3

Verdict: ACCEPTED