3228. Maximum Number of Operations to Move Ones to the End

class Solution {
public:
    int maxOperations(string s)
    {
        int res = 0, cnt = 0;
        for (int i = 0; i < s.size(); ++i)
        {
            if (s[i] == '1') ++cnt;
            else if (i > 0 && s[i - 1] == '1') res += cnt;
        }
        return res;
    }
};

• T: $O(N)$
• S: $O(1)$