5 Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: "cbbd"
Output: "bb"

一、逐一判断法

    public String longestPalindrome(String s) {
        String res;
        int left=0,right=0;
        int max=1;
        if(s.length()==0) return res="";
        for(int i=0;i<s.length();i++){
            for(int k=s.length()-1;k>i;k--){
                if(s.charAt(i)==s.charAt(k)){
                    int m=i;
                    int n=k;
                    if((k-i+1)%2==0){
                     while(m!=n-1){
                        if(s.charAt(m)!=s.charAt(n))
                            break;
                         m++;
                         n--;
                     }
                    if(m==n-1&&k-i+1>max&&s.charAt(m)==s.charAt(n)) {
                        max=k-i+1;
                        left=i;
                        right=k;
                     }
                    }
                    else{
                    while(m!=n){
                        if(s.charAt(m)!=s.charAt(n))
                            break;
                         m++;
                         n--;
                     }
                    if(m==n&&k-i+1>max) {
                        max=k-i+1;
                        left=i;
                        right=k;
                     }
                    }
                }
            }
        }
        res=s.substring(left,right+1);
        return res;
    }

先找出回文字串，再和保存好的最长回文子串的MAX值进行判断是否储存当前字串的信息。