每日一道leetcode：5. 最长回文子串

class Solution {
public:
    vector<int> cal(string s, int i, int j) {
        int n = s.length();
        while (i >= 0 && j < n && s[i] == s[j]) {
            i --;
            j ++;
        }
        return {i+1, j-1};
    }

    string longestPalindrome(string s) {
        int n = s.length();
        int left = 0, right = 0;
        int max_len = 0;
        for (int i = 0; i < n; i++) {
            vector<int> a = cal(s, i, i);
            vector<int> b = cal(s, i, i+1);
            if (a[1]-a[0]+1 > max_len) {
                left = a[0];
                right = a[1];
                max_len = a[1]-a[0]+1;
            }
            if (b[1]-b[0]+1 > max_len) {
                left = b[0];
                right = b[1];
                max_len = b[1]-b[0]+1;
            }
        }
        return s.substr(left,right-left+1);
    }
};