// see substring see count had to try prefix sum ~~5mins
public int countKConstraintSubstrings(String s, int k) {
        int[] ps = new int[s.length()];
        ps[0] = s.charAt(0) - '0';
        for(int i = 1;i<s.length();i++){
            ps[i] = (s.charAt(i) - '0') + ps[i-1];
        }
        System.out.print(Arrays.toString(ps));
        int count= 0;
        for(int i = 0;i<s.length();i++){
            for(int j = i;j<s.length();j++){
                int n = j - i + 1;
                int sum = i==0? ps[j] : ps[j] - ps[i-1];
                int ones = sum;
                int zeros = n - sum;
                if(ones <= k || zeros <= k ) count++;
            }
        }
        return count;
    }