題目描述

輸出描述：

思路

思路1：使用HashMap+StringBuilder

思路2：直接使用LinkedHashMap（有序的）。注意：LinkedHash的有序性是指插入的順序,TreeMap的有序性是自動按值排序

思路3：使用陣列實現一個簡單的Map

解法1

import java.util.*;
 
public class Solution {
    private Map<Character,Integer> map = new HashMap<>();
    private StringBuilder sb = new StringBuilder();
    //Insert one char from stringstream
    public void Insert(char ch) {
        sb.append(ch);
        map.put(ch,map.getOrDefault(ch,0) + 1);
    }
    //return the first appearence once char in current stringstream
 

    public char FirstAppearingOnce() {
        int index = 0;
        while (index < sb.length()){
            if (map.get(sb.charAt(index)) == 1){
                return sb.charAt(index);
            }
            index++;
        }
        return '#';
    }
}

解法2

import java.util.*;
public class
 
 Solution {
    Map<Character,Integer> map = new LinkedHashMap<>();
    //Insert one char from stringstream
    public void Insert(char ch) {
        map.put(ch,map.getOrDefault(ch,0) + 1);
    }
    //return the first appearence once char in current stringstream
    public char FirstAppearingOnce() {
        for (char c : map.keySet()){
            if (map.get(c) == 1)
                return c;
        }
        return '#';
    }
}

解法3

Mark