LeetCode: Count Number Of Homogenous Substrings Solution

Approach

Accumulated count for contiguous substring of the same characters

1"a" -> 1 (1)
2"aa" -> 3 (1 + 2)
3"aaa" -> 6 (1 + 2 + 3)

Implementation

1/**
2 * @param {string} s
3 * @return {number}
4 */
5var countHomogenous = function (s) {
6  let res = 0,
7    prev = "",
8    acc
9  for (const c of s) {
10    acc = c === prev ? acc + 1 : 1
11    prev = c
12    res += acc
13  }
14  return res % (1e9 + 7)
15}