LeetCode(3)

5. 

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

Example:

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Example:

Input: "cbbd"

Output: "bb"

这个解法里面很有意思的是一个扩散的方式，我自己做的时候 用的 是两层迅速，明显没有这个方式 快。

The performance is pretty good, surprisingly.

public class Solution {
private int lo, maxLen;

public String longestPalindrome(String s) {
	int len = s.length();
	if (len < 2)
		return s;
	
    for (int i = 0; i < len-1; i++) {
     	extendPalindrome(s, i, i);  //assume odd length, try to extend Palindrome as possible
     	extendPalindrome(s, i, i+1); //assume even length.
    }
    return s.substring(lo, lo + maxLen);
}

private void extendPalindrome(String s, int j, int k) {
	while (j >= 0 && k < s.length() && s.charAt(j) == s.charAt(k)) {
		j--;
		k++;
	}
	if (maxLen < k - j - 1) {
		lo = j + 1;
		maxLen = k - j - 1;
	}
}}

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我自己写的和人家写的区别：人家的performance 特别好， 只有一个全长度循环，还有一个 是半长度循环