Leetcode 5. Longest Palindromic Substring

Posted 2020-07-30 Deribs4

5. Longest Palindromic Substring

• Total Accepted: 128442
• Total Submissions: 539273
• Difficulty: Medium

 

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：Palindromic，就是回文的意思。一般回文字符串是从中间向两边展开，看中心的左边是否完全等于中心的右边。

 

代码：代码中有2处改进，需要体会。

 1 class Solution {
 2 public:
 3     string longestPalindrome(string s) {
 4         int minbegin = 0, maxlen = 1;
 5         for (int i = 0; i < s.size(); ) {
 6             //改进1
 7             if (i + maxlen / 2 >= s.size()) break;
 8             int begin = i, end = i;
 9             while (end < s.size() - 1 && s[end] == s[end+1]) end++;
10             //改进2
11             i = end + 1;
12             while (end < s.size() && begin >=0 && s[begin] == s[end]){
13                 begin--;
14                 end++;
15             }
16             int curlen = end - begin - 1;
17             if (curlen > maxlen) {
18                 maxlen = curlen;
19                 minbegin = begin + 1;
20             }
21         }
22         return s.substr(minbegin,maxlen);
23     }
24 };