[Leetcode]Longest Palindromic Substring

Longest Palindromic Substring 题解

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题目来源：https://leetcode.com/problems/longest-palindromic-substring/description/

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Description

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Input: "cbbd"

Output: "bb"

Solution

class Solution {
private:
    int resStart;
    int resSize;
    int inSize;
    void expandPalindrome(string& s, int start, int end) {
        while (start >= 0 && end < inSize && s[start] == s[end]) {
            start--;
            end++;
        }
        start++;
        int temp = end - start;
        if (temp > resSize) {
            resSize = temp;
            resStart = start;
        }
    }
public:
    string longestPalindrome(string s) {
        inSize = s.length();
        if (inSize <= 1)
            return s;
        resStart = resSize = 0;
        for (int i = 0; i < inSize - 1; i++) {
            expandPalindrome(s, i, i); // 求奇数长度的回文子串
            expandPalindrome(s, i, i + 1); // 求偶数长度的回文子串
        }
        return s.substr(resStart, resSize);
    }
};

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解题描述

这道题考察的是求一个字符串中的最长回文子串。而对每一个非空的输入串来说，其回文子串最短为1，因此可以对字符串中的每一个元素，同时向左和向右探测，直到回文子串结束，每次判断得到的子串是否是最长的即可。