1513.NumSub.cs

// 1513. Number of Substrings With Only 1s
// Given a binary string s, return the number of substrings with all characters 1's. Since the answer may be too large, return it modulo 109 + 7.
// Example 1:
// Input: s = "0110111"
// Output: 9
// Explanation: There are 9 substring in total with only 1's characters.
// "1" -> 5 times.
// "11" -> 3 times.
// "111" -> 1 time.
// Example 2:
// Input: s = "101"
// Output: 2
// Explanation: Substring "1" is shown 2 times in s.
// Example 3:
// Input: s = "111111"
// Output: 21
// Explanation: Each substring contains only 1's characters.

public class Solution {
    public int NumSub(string s) {
        long result = 0;
        int count = 0;
        foreach(char c in s){
            if(c == '1') result += ++ count;
            else count = 0;
        }
        return (int)(result%1000000007);
    }
}