【LeeCode】5. 最长回文子串

【题目描述】

给你一个字符串 ​​s​​，找到 ​​s​​ 中最长的回文子串。

​​https://leetcode.cn/problems/longest-palindromic-substring/?favorite=2cktkvj​​

【示例】

【代码 -- 133/143】

package com.company;
import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;


public class threeSum {
    public static void main(String[] args) {
        String str = "babad";
        String str1 = "a";
//        String str2 = "cbbd";
        String str2 = "aacabdkacaa";
        String str3 = "bb";
        String str4 = "ccc";     // ccc
//        longestPalindrome(str);
//        longestPalindrome(str1);
        System.out.println(longestPalindrome(str2));
//        longestPalindrome(str3);
//        longestPalindrome(str4);

    }

    public static String longestPalindrome(String s) {

        String result = null;
        List<String> list = new ArrayList<>();
        if(huiwen(s)){
            result = s;
            return result;
        }
        int max = Integer.MIN_VALUE;
        for(int i = 0; i < s.length(); i++){
            for(int j = i + 2; j <= s.length(); j++){
                String ss = s.substring(i, j);
                if(huiwen(ss)){
                    if(ss.length() >= max){
                        max = ss.length();
                        list.add(ss);
                    }
                }
            }
        }

        if(list.size() > 0){
            result = list.get(list.size() - 1);
        }else{
            result = s.charAt(0)+"";
        }
        return  result;
    }

    private static boolean huiwen(String s) {
        boolean flag = false;
        String x = new StringBuilder(s).reverse().toString();
        if(x.equals(s)){
            flag = true;
        }
        return flag;
    }
}