LeetCode 5 Longest Palindromic Substring

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, and there exists one unique longest palindromic substring.

 

思路：这道题采用遍历法，分两种情况考虑；

1.ada类型

2.aadd类型

对于上述两种类型，分别以k、k+1索引 或者k、k+2索引来判断，然后设置两个标记 i、j 索引，分别向两边计数，当出现j-i有最大值时，返回该索引。

代码如下：

 

public class Solution {    public String longestPalindrome(String s) {    int length =s.length();    int max1=0,max2=0;//记录两个索引    int len = 0;    if(length == 2 && s.charAt(0)==s.charAt(1)||length ==1){         return s;    }    for (int k = 0; k < length-1; k++) {if(s.charAt(k)==s.charAt(k+1)){if(len<=1){max1 = k;max2 =k+1;len = 1;}int i = k-1;int j = k+2;while(i>=0&&j<=length-1){if(s.charAt(i)==s.charAt(j)){if(j-i>len){max1 = i;max2 = j;len = max2 - max1;}i--;j++;}else{break;}}}if(k+2>=length){continue;}if (s.charAt(k)==s.charAt(k+2)) {if(len<=2){max1 = k;max2 =k+2;len = 2;}int i = k-1;int j = k+3;while(i>=0&&j<=length-1){if(s.charAt(i)==s.charAt(j)){if(j-i>len){max1 = i;max2 = j;len = max2 - max1;}i--;j++;}else{break;}}}}return s.substring(max1, max2+1);    }}

这里有个优化算法，值得一看

http://www.cnblogs.com/bitzhuwei/p/Longest-Palindromic-Substring-Part-II.html