思维

看每个0的左边有多少个1

class Solution {
public:
    typedef long long LL;
    long long minimumSteps(string s) {
        LL res = 0;
        for (int i = 0, cnt = 0; i < s.size(); i ++ ) 
            if (s[i] == '0') res += cnt;
            else cnt ++ ;
        return res; 
    }
};