README_EN.md

424. Longest Repeating Character Replacement

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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

Solutions

Python3

class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        counter = [0] * 26
        i = j = maxCnt = 0
        while i < len(s):
            counter[ord(s[i]) - ord('A')] += 1
            maxCnt = max(maxCnt, counter[ord(s[i]) - ord('A')])
            if i - j + 1 > maxCnt + k:
                counter[ord(s[j]) - ord('A')] -= 1
                j += 1
            i += 1
        return i - j

Java

class Solution {
    public int characterReplacement(String s, int k) {
        int[] counter = new int[26];
        int i = 0;
        int j = 0;
        for (int maxCnt = 0; i < s.length(); ++i) {
            char c = s.charAt(i);
            ++counter[c - 'A'];
            maxCnt = Math.max(maxCnt, counter[c - 'A']);
            if (i - j + 1 - maxCnt > k) {
                --counter[s.charAt(j) - 'A'];
                ++j;
            }
        }
        return i - j;
    }
}

C++

class Solution {
public:
    int characterReplacement(string s, int k) {
        vector<int> counter(26);
        int i = 0, j = 0, maxCnt = 0;
        for (char& c : s) {
            ++counter[c - 'A'];
            maxCnt = max(maxCnt, counter[c - 'A']);
            if (i - j + 1 > maxCnt + k) {
                --counter[s[j] - 'A'];
                ++j;
            }
            ++i;
        }
        return i - j;
    }
};

Go

func characterReplacement(s string, k int) int {
	counter := make([]int, 26)
	j, maxCnt := 0, 0
	for i := range s {
		c := s[i] - 'A'
		counter[c]++
		if maxCnt < counter[c] {
			maxCnt = counter[c]
		}
		if i-j+1 > maxCnt+k {
			counter[s[j]-'A']--
			j++
		}
	}
	return len(s) - j
}

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