【Easy】627. Longest Palindrome

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.

Notice Assume the length of given string will not exceed 1010.

Example:

Given s = "abccccdd" return 7

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

解题思路

找出一共有几对，加上一个单身的。

核心代码

    Set<Character> set = new HashSet<>();
    int result = 0;

    for (int i = 0; i < s.length(); i++){
        if (set.contains(s.charAt(i))){
            set.remove(s.charAt(i));
            result += 2;
        } else {
            set.add(s.charAt(i));
        }
    }

    return result + (set.size() > 0 ? 1 : 0);

时间空间复杂度

O(n) + S(n)

n为数组长度