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# LeetCode 424. Longest Repeating Character Replacement (javascript solution)

### 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.

### Solution:

Time Complexity : O(n)
Space Complexity: O(n)

``````var characterReplacement = function(s, k) {
// Keep count of all the characters in the string
const chars = {}
// left pointer, character with the current max frequency, return value
let left = 0, maxf = 0, output = 0
for(let right = 0; right < s.length; right++) {
const char = s[right]
// Increment count of the current character
chars[char] = 1 + (chars[char] || 0)
// Update the character frequency
maxf = Math.max(maxf, chars[char])
// Shrink the window of characters we are looking at until we can have a window of all the same characters + k charcters to change
while((right-left+1) - maxf > k) {
chars[s[left]] -= 1
left++
}
// Update the output if the current window is greater than our previous max window
output = Math.max(output, right - left +1)
}
return output
};
``````