标签：problems mes with 链接 letters could turn blog output
原题链接在这里：https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/
题目：
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.
题解：
To make sure every char in substring appears no less than k time, we need to make sure unique count == no less than k count.
We could add one more argument uniTargetCnt, that is the target of count of unique char.
First move the runner.
While unique count > target, move the walker.
Update the longest with target unique count.
target unique count could be [1, 26].
Time Complexity: O(n). n = s.length().
Space: O(1).
AC Java:
1 class Solution { 2 public int longestSubstring(String s, int k) { 3 if(s == null || s.length() == 0 || k <= 0){ 4 return 0; 5 } 6 7 int res = 0; 8 for(int i = 1; i <= 26; i++){ 9 res = Math.max(res, longestTargetSubstring(s, k, i)); 10 } 11 12 return res; 13 } 14 15 private int longestTargetSubstring(String s, int k, int uniTargetCnt){ 16 int walker = 0; 17 int runner = 0; 18 int [] map = new int[26]; 19 int uniCnt = 0; 20 int overKCnt = 0; 21 int res = 0; 22 23 while(runner < s.length()){ 24 if(map[s.charAt(runner) - ‘a‘]++ == 0){ 25 uniCnt++; 26 } 27 28 if(map[s.charAt(runner++) - ‘a‘] == k){ 29 overKCnt++; 30 } 31 32 while(uniCnt > uniTargetCnt){ 33 if(map[s.charAt(walker) - ‘a‘]-- == k){ 34 overKCnt--; 35 } 36 37 if(map[s.charAt(walker++) - ‘a‘] == 0){ 38 uniCnt--; 39 } 40 } 41 42 if(uniCnt == uniTargetCnt && uniCnt == overKCnt){ 43 res = Math.max(res, runner - walker); 44 } 45 } 46 47 return res; 48 } 49 }
LeetCode 395. Longest Substring with At Least K Repeating Characters
标签：problems mes with 链接 letters could turn blog output
原文地址：https://www.cnblogs.com/Dylan-Java-NYC/p/12155767.html
