题目描述:

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:

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Input:
"abccccdd"

Output:
7

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

给出一个字符数组, 问从中取出字符拼成的回文串最长是多少. 这道题比较简单, 回文串中的字符都是成对出现的, 因此如果一个字母的数量超过了2, 那么它就一定可以放在回文串中, 数量则是必须是偶数奇数的话则减1. 最后看是否还有剩下的字母, 如果有就可以选一个放在中间.

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class Solution {
public:
    int longestPalindrome(string s) {
        vector<int> letters(52, 0);
        for(auto i : s){
            if(i >= 'a' && i <= 'z'){
                letters[i - 'a']++;
            }
            else{
                letters[i - 'A' + 26]++;
            }
        }
        int ans = 0;
        for(auto i : letters){
            if(i > 1){
                ans += i % 2 ? i - 1 : i;
            }
        }
        if(ans < s.length()) ans++;
        return ans;
    }
};