Leetcode 5. Longest Palindromic Substring

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。

class Solution {
public:
    string longestPalindrome(string s) {
        int minbegin = 0, maxlen = 1;
        for (int i = 0; i < s.size(); ) {
            //改进1
            if (i + maxlen / 2 >= s.size()) break;
            int begin = i, end = i;
            while (end < s.size() - 1 && s[end] == s[end+1]) end++;
            //改进2
            i = end + 1;
            while (end < s.size() && begin >=0 && s[begin] == s[end]){
                begin--;
                end++;
            }
            int curlen = end - begin - 1;
            if (curlen > maxlen) {
                maxlen = curlen;
                minbegin = begin + 1;
            }
        }
        return s.substr(minbegin,maxlen);
    }
};