题解 | #字符流中第一个不重复的字符#

import java.util.*;
public class Solution {
    //Insert one char from stringstream
    //HashMap判断是否重复
    //队列Que给出第一个不重复的字符
    static HashMap<Character, Boolean> map = new HashMap<Character, Boolean>();
    static Queue<Character> que = new LinkedList<Character>();
    public void Insert(char ch)
    {
    //判断是否重复
    //重复，则char键对应的boolean值为false，否则为true
        if(map.containsKey(ch)){
            map.put(ch, false);
        }else {
            map.put(ch, true);
            que.offer(ch);
        }
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce()
    {
        while(!que.isEmpty()){
        //非空且que.peek()对应的值为false，poll
            if(map.get(que.peek()).equals(false)){
                que.poll();
                continue;
            }
       //非空且que.peek()对应的值为true，返回peek()
            return (char)que.peek();
        }
        //队列为空，不存在不重复的数字，返回"#"
        return '#';
    }
}