409. Longest Palindrome

Posted 2021-01-20 ruruozhenhao

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.

 

 Approach #1: C++.

class Solution {
public:
    int longestPalindrome(string s) {
        unordered_map<char, int> mp;
        int nums = 0;
        bool flag = false;
        for (int i = 0; i < s.length(); ++i) 
            mp[s[i]]++;
        for (auto it = mp.begin(); it != mp.end(); ++it) {
            nums += it->second/2 * 2;
            if (it->second % 2 != 0 && !flag) 
                flag = true;
        }
        if (flag) nums++;
        return nums;
    }
private:
    static bool cmp(int a, int b) {
        return a >= b;
    }
};

　　

Approach #2: Java.

class Solution {
    public int longestPalindrome(String s) {
        int[] count = new int[128];
        for (char c : s.toCharArray()) 
            count[c]++;
        int ans = 0;
        for (int v : count) {
            ans += v / 2 * 2;
            if (ans % 2 == 0 && v % 2 == 1)
                ans++;
        }
        return ans;
    }
}

　　

Approach #3: Python.

class Solution(object):
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: int
        """
        ans = 0
        for v in collections.Counter(s).itervalues():
            ans += v / 2 * 2
            if ans % 2 == 0 and v % 2 == 1:
                ans += 1
            
        return ans

　　

Time Submitted	Status	Runtime	Language
a few seconds ago	Accepted	44 ms	python
2 minutes ago	Accepted	5 ms	java
5 minutes ago	Accepted	8 ms	cpp