Leetcode 395. Longest Substring with At Least K Repeating Characters 至少K重复最长子序列 解题报告

1 解题思想

2 原题

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.

3 AC解

public class Solution {
public int longestSubstring(String s, int k) {
//System.out.println(s);
int n = s.length();
if(n < k) return 0;
int counter[] = new int[26];
boolean valid[] = new boolean[26];
char ss[] = s.toCharArray();
//统计每个字符的长度
for(int i=0;i<n;i++)
counter[ss[i] - 'a']++;
//检查当前字符串是否是完全满足的
boolean fullValid = true;
//判断每个字符的出现条件是否合适，即，要么不出现，要么出现了不少于k
for(int i=0;i<26;i++){
if(counter[i]>0 && counter[i]<k){
valid[i] = false;
fullValid = false;
}
else valid[i] = true;
}
if(fullValid) return s.length();
int max = 0;
int lastStart=0;
//把不符合要求的断开，然后依次检查 取最大
for(int i=0;i<n;i++){
if(valid[ss[i] - 'a'] == false){
// System.out.println(lastStart+"  "+i);
max = Math.max(max,longestSubstring(s.substring(lastStart,i),k));
lastStart = i + 1;
}
}
max = Math.max(max,longestSubstring(s.substring(lastStart,n),k));
return max;

}
}