424. Longest Repeating Character Replacement

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

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

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)
⏱️ Thời gian O(n)
💾 Không gian O(n)

💻 Lời Giải

Python 0424-longest-repeating-character-replacement.py 
class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        n = len(s)
        j = 0
        maxFreq, maxLeng = 0, 0
        d = defaultdict(int)
        
        for i in range(n):
            d[s[i]] += 1
            maxFreq = max(maxFreq, d[s[i]])
            while i - j + 1 - maxFreq > k:
                d[s[j]] -= 1
                j += 1
            maxLeng = max(maxLeng, i - j + 1)
        
        return maxLeng