[Leetcode] Longest Palindromic Substring (Java)

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.

找回文子串，从中心找起，向两边扩张，分情况讨论：

1）偶数 如abba；

2）奇数 如aba。

public class LongestPalindromicSubstring {
	public String longestPalindrome(String s) {
		int max = 1;
		int maxI = 0;
		boolean[] flag = new boolean[s.length()];
		for(int i=0;i<s.length();i++) {
			int temp = 1;
			int pre=i-1,post=i+1;
			while(pre>=0 && post<=s.length()-1 && s.charAt(pre)==s.charAt(post)) {
				temp+=2;
				pre--;
				post++;
			}
			if(temp>max){
				max=temp;
				maxI = i;
				flag[i] = false;
			}
			pre=i;
			post=i+1;
			temp=0;
			while(pre>=0 && post<=s.length()-1 && s.charAt(pre)==s.charAt(post)) {
				temp+=2;
				pre--;
				post++;
			}
			if(temp>max) {
				max=temp;
				maxI=i;
				flag[i] = true;
			}
		}
		if(flag[maxI])
			return s.substring(maxI-max/2+1,maxI+max/2+1);
		else 
			return s.substring(maxI-max/2, maxI+max/2+1);
	}
	public static void main(String[] args) {
		String s = "awwtwywertyu";
		System.out.println(new LongestPalindromicSubstring().longestPalindrome(s));
	}
}