409. Longest Palindrome 求最長的迴文序列

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.

給定一個字符串包含小寫或大寫字母，找到可以與那些最長的迴文序列長度。

這是大小寫敏感的，例如“Aa”不是在這裏不是迴文序列。

筆記
假設給定字符串的長度不超過1010。

example

Input:
"abccccdd"

Output:
7

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

solution

public int longestPalindrome(String s) {
        boolean[] map = new boolean[128];
        int len = 0;
        for (char c : s.toCharArray()) {
            map[c] = !map[c];         // flip on each occurrence, false when seen n*2 times
            if (!map[c]) len+=2;
        }
        if (len < s.length()) len++; // if more than len, atleast one single is present
        return len;
    }