In this Leetcode Longest Repeating Character Replacement problem solution, 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.

Leetcode Longest Repeating Character Replacement problem solution


Problem solution in Python.

class Solution(object):
	def characterReplacement(self, s, k):
		"""
		:type s: str
		:type k: int
		:rtype: int
		using the sliding window technique
		"""
		window_start = 0
		longest_substring, most_repeated = 0 , 0
		freq_map = {}

		for window_end in range(len(s)):
			curr_char = s[window_end]
			if curr_char not in freq_map:
				freq_map[curr_char] = 0
			freq_map[curr_char] += 1

			most_repeated = max(most_repeated, freq_map[curr_char])

			if window_end - window_start + 1 - most_repeated > k:
				left_char = s[window_start]
				freq_map[left_char] -= 1
				window_start += 1
			longest_substring = max(longest_substring, window_end - window_start + 1)

		return longest_substring


Problem solution in Java.

public int characterReplacement(String s, int k) {
int start=0;
int longCharCount=0;
Map<Character, Integer> map = new HashMap<>();
int maxLength=0;

    for(int end=0;end<s.length();end++){
        char endchar = s.charAt(end);
        map.put(endchar, map.getOrDefault(endchar,0)+1);
        longCharCount = Math.max(longCharCount, map.get(endchar));
        
        if(end-start+1-longCharCount >k){
            char startChar=s.charAt(start);
            map.put(startChar, map.getOrDefault(startChar,0)-1);
            start++;
        }
        
        maxLength = Math.max(maxLength, end-start+1);
    }
    
    return maxLength;

}


Problem solution in C++.

class Solution {
public:
    int characterReplacement(string s, int k) {
        int size = s.size(); int ret = 0;
        vector<int> count(26, 0);
        int start = 0; int end = 0; int Freq = 0; 
        for(; end<size; end++){
            count[s[end]-'A'] += 1;
            Freq = max(Freq, count[s[end]-'A']);
            while((end-start+1)-Freq > k) {
               
                count[s[start]-'A'] -= 1;
                start += 1;
                
            }
            ret=max(ret,end-start+1);
        }
        return ret;
    }
};


Problem solution in C.

int characterReplacement(char * s, int k){
    if(s[0]==0)return 0;
    int n=strlen(s);
    int max=0;
    int i;
    int diff=0;
    int *record=calloc(26,4);
    int l;
    
    for(i=0,l=0;i<n;i++){
        if(++record[s[i]-'A']<=max){
            if(diff==k){
                record[s[l++]-'A']--;
            }
            else{
                diff++;
            }
        }
        else {
            max++;
        }   
    }    
    return max+diff;
}