Longest Palindromic Substring

最长回文子串

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暴力匹配
Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.

Have you met this question in a real interview? Yes
Example
Given the string = “abcdzdcab”, return “cdzdc”.

Challenge
O(n2) time is acceptable. Can you do it in O(n) time.

public class Solution {
    /**
     * @param s input string
     * @return the longest palindromic substring
     */
    public String longestPalindrome(String s) {
        // Write your code here
        String result = new String();
        if(s==null||s.isEmpty())return result;

        int n = s.length();
        int longest =0;
        int left=0,right=0;
        for(int i = 0;i<n;i++){
            for(int j = i+1;j<=n;j++){
                String substr = s.substring(i,j);
                if(isPalindrome(substr)&&substr.length()>longest){
                    longest =substr.length();
                    left =i;
                    right =j;
                }
            }
    }
    result = s.substring(left,right);
    return result ;
}
    private boolean isPalindrome(String s){
        if(s==null||s.isEmpty())return false;
        int n = s.length();
        for (int i = 0;i<n;i++){
            if(s.charAt(i)!=s.charAt(n-i-1))return false;

        }
        return true;

    }
}