public class Solution
extends Object
1513 - Number of Substrings With Only 1s\.
Medium
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.
**Constraints:**
* 1 <= s.length <= 105
* `s[i]` is either `'0'` or `'1'`.