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"

 

查找最长的回文子串，这道题比较简单，方法也很多，不多说了。

 1 public class Solution {
 2     public string LongestPalindrome(string s) {
 3         if (string.IsNullOrEmpty(s)) return s;
 4         string result = s[0].ToString();
 5         for (int i = 1; i < s.Length; i++)
 6         {
 7             int tmp = 0;
 8             while (tmp < i && tmp < s.Length - i && s[i - tmp - 1] == s[i + tmp])
 9                 tmp++;
10             if (tmp > 0)
11                 if (tmp * 2 > result.Length)
12                     result = s.Substring(i - tmp, tmp * 2);
13 
14             if (i >= s.Length - 1) continue;
15 
16             tmp = 0;
17             while (tmp < i && tmp < s.Length - 1 - i && s[i - tmp - 1] == s[i + tmp + 1])
18                 tmp++;
19             if (tmp > 0)
20                 if (tmp * 2 + 1 > result.Length)
21                     result = s.Substring(i - tmp, tmp * 2 + 1);
22         }
23         return result;
24     }
25 }