Longest Substring with At Least K Repeating Characters

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 · 1.3k 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#leetcode #递归

leetcode 专栏收录该内容

175 篇文章

订阅专栏

本文介绍了一种寻找字符串中每个字符至少重复k次的最长子串的算法。通过扫描并使用分隔符来划分原问题为子问题进行递归求解，提供了完整的Java实现代码。

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.

这个题蛮力法肯定不行，思路是扫描出现次数小于k的字母，然后将它们作为分隔符，然后就将这些子串划分成原问题的子问题，递归求解。

public class Solution {
    public int longestSubstring(String s, int k) {
        if(k<=1){
            return s.length();
        }
        
        int[] repeat=new int[26];
        for(int i=0;i<s.length();i++){
            repeat[s.charAt(i)-'a']++;
        }
        StringBuilder reg=new StringBuilder("");
        boolean firstSplit=true;
        for(int i=0;i<26;i++){
            if(repeat[i]>0&&repeat[i]<k){
                if(firstSplit){
                    reg.append((char)(i+'a'));
                    firstSplit=false;
                }
                else{
                    reg.append("|"+(char)(i+'a'));
                }
            }
        }
        if(reg.length()>0){
            //说明有分隔符
            String[] strs=s.split(reg.toString());
            int max=0;
            int tmpAns=0;
            for(String str:strs){
                tmpAns=longestSubstring(str, k);
                if(tmpAns>max){
                    max=tmpAns;
                }
            }
            return max;
        }
        else{
            //没有分隔符,说明s中的每一个字符出现的次数都大于等于k
            return s.length();
        }
    }
}