算法珠玑——最长回文子串(5)

算法珠玑——最长回文子串(5)

三指针?

/*
 * @lc app=leetcode.cn id=5 lang=cpp
 *
 * [5] 最长回文子串
 */

// @lc code=start
class Solution {
public:
    string longestPalindrome(string s) {
        int n = s.length();
        
        // (object) base for end case: start and mxlen
        int mxlen = 0, start = 0;

        int left, right;
        // (base/end)induction step: itertive
        for (int i = 0; i < n; ++i)
        {
            left = i;
            right = i;
            
            // sub induction step: shift right
            while (right+1 < n && s[right] == s[right+1]) 
                ++right;

            // sub induction step: adjust left and right
            while (left-1 >= 0 && right+1 < n && s[left-1] == s[right+1]) 
            {
                --left; 
                ++right;
            }

            // sub induction step: set start and maxlen
            if (mxlen < right-left+1) 
            {
                mxlen = right-left+1;
                start = left;
            }
        }
        // end case
        return s.substr(start, mxlen);
    }
};
// @lc code=end