LeetCode_ 409_ Longest palindrome string

Topic link

• https://leetcode.cn/problems/longest-palindrome/

Title Description

Given a string of uppercase and lowercase letters s , return Constructed from these letters The longest palindrome string .

In the process of construction , Please note that Case sensitive . such as "Aa" Can't be treated as a palindrome string .

Example 1:

 Input :s = "abccccdd"
 Output :7
 explain :
 The longest palindrome string we can construct is "dccaccd",  Its length is  7.

Example 2:

 Input :s = "a"
 Input :1

Example 3:

 Input :s = "bb"
 Input : 2

Tips :

1 <= s.length <= 2000
s  Only lowercase and / Or capital letters 

Their thinking

• Traversal string , And use HashSet To record , If it doesn't appear, save it in set in , If it happens , Then turn the letters that have appeared from set Delete in , And put the answer +2
• Last set There are odd numbers of letters stored in , Judge set Whether the set is empty , If it's not empty , Just put the answer +1

AC Code

class Solution {
    
    public int longestPalindrome(String s) {
    
        int ans = 0;
        HashSet<Character> set = new HashSet<>();
        for (int i = 0; i < s.length(); i++) {
    
            char c = s.charAt(i);
            if (set.contains(c)) {
    
                set.remove(c);
                ans += 2;
            } else {
    
                set.add(c);
            }
        }
        if (set.size() > 0) {
    
            ans += 1;
        }
        return ans;
    }
}