Longest Substring with At Least K Repeating Characters LeetCode solution in JavaScript

1
var longestSubstring = function (s, k) {
2
  let n = s.length;
3
  if (n == 0 || n < k) return 0;
4
  if (k == 1) return n;
5

6
  const freq = {}; // object to store the freq of each character ex . { 'a' : 2 , 'b' : 1 ...}
7

8
  // counting the freq. of each character
9
  for (let i = 0; i < n; i++) {
10
    let char = s[i];
11
    if (freq[char])
12
      // if the character is already present , increase it's freq.
13
      freq[char]++;
14
    else freq[char] = 1; // else assign the freq. as 1
15
  }
16
  let i = 0;
17
  while (i < n && freq[s[i]] >= k)
18
    // while loop continue till the freq. of character is greater than or equal to k
19
    i++;
20

21
  if (i >= n - 1)
22
    // if i == string.length
23
    return i;
24

25
  let left1 = longestSubstring(s.substring(0, i), k); // dividing the string at index where freq. of character is less than k and calling the func again on the substring
26

27
  while (i < n && freq[s[i]] < k)
28
    // ignore the char whose freq. is less than k
29
    i++;
30

31
  let right1 = longestSubstring(s.substring(i), k); // second part of the string
32

33
  return Math.max(left1, right1);
34
};