LeetCode

问题

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

代码

class Solution {public:    int longestPalindrome(string s) {        vector<int> v(58,0);    // A-z 65-122，因此开辟58个空间即可        int flag = 0, length = 0;        for(int i=0; i<s.size(); i++)            v[s[i]-65]++;        for(int j=0; j<58; j++)        {            if(v[j] == 1) flag = 1;            else if(v[j])            {                if(v[j]%2 == 0) length += v[j];                else                 {                    length += (v[j]-1);                    flag = 1;                }            }        }        if(flag) length++;        return length;    }    //参考答案，贵在精简，不过时间复杂度一样O（n^2），空间花费多一些    int longestPalindrome(string s) {        vector<int> m(256, 0);                for (auto& c : s) m[c-'\0']++;        int result = 0;        for (auto& i : m) result += i%2 ? (result%2 ? i-1 : i) : i; //result%2判断是否已经采用过奇数个数的字母        return result;    }};