LeetCode 424. Longest Repeating Character Replacement 滑动窗口

最新推荐文章于 2025-02-03 15:37:10 发布

原创最新推荐文章于 2025-02-03 15:37:10 发布 · 170 阅读

0 ·

CC 4.0 BY-SA版权

leetcode 同时被 2 个专栏收录

231 篇文章

订阅专栏

python3

120 篇文章

订阅专栏

给定一个只包含大写字母的字符串s和整数k，你可以进行最多k次操作，每次操作可以选择字符串中的一个字符并将其替换为任意其他大写字母。找出在进行这些操作后，最长的子串，该子串中所有字符都相同。这个问题可以通过滑动窗口和哈希映射来解决，通过维护窗口内的最大频率，逐步扩大窗口直至无法满足条件再移动左边界。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

Given a string s that consists of only uppercase English letters, you can perform at most k operations on that string.

In one operation, you can choose any character of the string and change it to any other uppercase English character.

Find the length of the longest sub-string containing all repeating letters you can get after performing the above operations.

Note:
Both the string's length and k will not exceed 104.

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.

----------------------------------------------

滑动窗口内字符出现最高的频率是maxn，那么maxn一定满足r-l-maxn<=k，而算maxn的操作对于每次滑动来说是O(1)的。

因此，在满足r-l-maxn<=k，尝试扩大右边界，尝试能否找到更大的maxn；如果没法满足r-l-max<=k，左右边界同时向右移动

from collections import defaultdict

class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        l, r, slen, maxn = 0, 0, len(s), 0
        dic = defaultdict(int)
        while (r < slen):
            dic[s[r]] += 1
            maxn = max(maxn, dic[s[r]])
            if (r - l + 1 - maxn > k):
                dic[s[l]] -= 1
                l += 1
            r += 1
        return r - l