【LeetCode 409】关关的刷题日记31Longest Palindrome- 专知

【LeetCode 409】关关的刷题日记31Longest Palindrome

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关关的刷题日记31 – Leetcode 409. Longest Palindrome

题目

Given a string which consists of lowercase or uppercase letters, find the length of the longest palindromes that can be built with those letters.

This is case sensitive, for example "Aa" is not considered a palindrome here.

Note: Assume the length of given string will not exceed 1,010.

Example:

Input: "abccccdd"

Output: 7

Explanation: One longest palindrome that can be built is "dccaccd", whose length is 7.

题目要求找出一个字符串能够成的最大回文长度。

思路

思路：如果字符数目是偶数的话，那么该字符都可以加入构成回文。如果字符数目是奇数的话，那么只有偶数个该字符可以加入构成回文。还需要注意的是，如果出现了总共有奇数个的字符，最后可以选一个放在回文最中间位置。

class Solution {public:    int longestPalindrome(string s) {        map<char,int>m;        for(char x:s)        {            m[x]++;        }        int re=0, flag=0;        for(auto x:m)        {            if(x.second%2==0)                re+=x.second;            else            {                re+=x.second-1;                flag=1;            }        }        return re+flag;    }};