题解 | #字符流中第一个不重复的字符#

import java.util.*;

public class Solution {

    HashMap<Character, Integer> map = new HashMap<>();
    Queue<Character> queue = new LinkedList<>();

    //Insert one char from stringstream
    public void Insert(char ch)
    {
        int count = map.getOrDefault(ch, 0);

        if (count == 0) {
            queue.offer(ch);
        } else {
            queue.remove(ch);
        }

        map.put(ch, count + 1);
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce()
    {
        return queue.isEmpty() ? '#' : queue.peek();
    }
}