LeetCode 5. 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.

Example 1:

Input: “babad”
Output: “bab”
Note: “aba” is also a valid answer.
Example 2:

Input: “cbbd”
Output: “bb”
*/

首先想到的是动态规划，单看到字符串长度差不多1000，遂放弃使用，看了大佬的解题思路回文子串问题,才发现还有另外一种思路，在写一个函数用来判断奇偶回文问题
子串长度为奇数："aba"判断两边即可，中心点在b
子串长度为偶数："abba"判断两边即可，中心点在两个字母bb之间

static int x = []() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(0);
    return 0;
}();

class Solution {
public:
    int exporta(string s, int L, int R){
        while(L >= 0 && R < s.size() && s.at(L) == s.at(R)){
            L--;
            R++;
        }
        return R-L-1;
    }
public:
    string longestPalindrome(string s) {
        if(s.length() < 1){
            return "";
        }
        int start = 0, end = 0;
        for(int i = 0; i < s.size(); i++){
            int len1 = exporta(s, i, i);
            int len2 = exporta(s, i, i+1);
            int len = max(len1, len2);
            if(len > end-start){
                start = i - (len-1)/2;
                end = i + len/2;
            }
        }
        return s.substr(start, end-start+1);
        //此处需注意substr的参数是返回从index开始的长度为num的字符串
    }
};