Longest Repeating Character Replacement
Description
You are given a string s
and an integer k
. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k
times.
Return the length of the longest substring containing the same letter you can get after performing the above operations.
Example 1:
Input: s = "ABAB", k = 2 Output: 4 Explanation: Replace the two 'A's with two 'B's or vice versa.
Example 2:
Input: s = "AABABBA", k = 1 Output: 4 Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA". The substring "BBBB" has the longest repeating letters, which is 4.
Constraints:
1 <= s.length <= 105
s
consists of only uppercase English letters.0 <= k <= s.length
Solution(javascript)
/**
* @param {string} s
* @param {number} k
* @return {number}
*/
var characterReplacement = function(s, k) {
// if empty string
if (!s || s.length === 0) return 0;
// Track letters
let map = {};
let max = 0;
let currentCountMax = 0;
let left = 0;
let currentLetter;
for (let i = 0; i < s.length; i++) {
currentLetter = s[i];
// Count the occurence of the current letter (in the present window)
// Track num of char occurances
map[currentLetter] ? map[currentLetter]++ : map[currentLetter] = 1;
// Update cur_count_max (in the present window)
if(map[currentLetter] > currentCountMax) currentCountMax = map[currentLetter];
// Sliding window: Check if the window we are checking is valid or not
// In case the size of window is bigger than cur_count_max plus max change(k)
// decrease the count of the leftmost letter and then slide left (left++)
if (i - left + 1 > currentCountMax + k) {
map[s[left]] -= 1;
left++
} else {
max = Math.max(max, i - left + 1)
}
}
return max;
};