0395-longest-substring-with-at-least-k-repeating-characters.adoc

395. Longest Substring with At Least K Repeating Characters

{leetcode}/problems/longest-substring-with-at-least-k-repeating-characters/[LeetCode - Longest Substring with At Least K Repeating Characters^]

Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times.

Example 1:

Input:
s = "aaabb", k = 3

Output:
3

The longest substring is "aaa", as 'a' is repeated 3 times.

Example 1:

Input:
s = "ababbc", k = 2

Output:
5

The longest substring is "ababb", as 'a' is repeated 2 times and 'b' is repeated 3 times.

解题思路：递归拆分子串，分治。先统计出每个字符出现的频次，维护一对双指针，从首尾开始统计，从首尾往中间排除，如果出现次数小于k则不可能出现在最终子串中，排除并挪动指针，然后得到临时子串，依次从头遍历，一旦发现出现频次小于k的字符，以该字符为分割线，分别递归求其最大值返回。

参考资料

1. Java递归 - 至少有K个重复字符的最长子串 - 力扣（LeetCode）

Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times.

Example 1:

Input:
s = "aaabb", k = 3

Output:
3

The longest substring is "aaa", as 'a' is repeated 3 times.

Example 2:

Input:
s = "ababbc", k = 2

Output:
5

The longest substring is "ababb", as 'a' is repeated 2 times and 'b' is repeated 3 times.

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