package LeetCode_1513
/**
* 1513. Number of Substrings With Only 1s
* https://leetcode.com/problems/number-of-substrings-with-only-1s/
*
Given a binary string s (a string consisting only of '0' and '1's).
Return the number of substrings with all characters 1's.
Since the answer may be too large, return it modulo 10^9 + 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.
Example 4:
Input: s = "000"
Output: 0
Constraints:
1. s[i] == '0' or s[i] == '1'
2. 1 <= s.length <= 10^5
* */
class Solution {
/*
* solution: keep counting the consecutive 1 then update countOne and result, but reset countOne=0 when encounter 0
* Time:O(n), Space:O(1)
* */
fun numSub(s: String): Int {
var result = 0
var countOne = 0
val mod = 1000000007
for (c in s) {
if (c == '1') {
countOne++
} else {
countOne = 0
}
result = (result + countOne) % mod
}
return result
}
}
