剑指Offer打卡day 41—— Acwing 64. 字符流中第一个只出现一次的字符

Posted 2021-05-24 Johnny*

【题目描述】

Acwing 64. 字符流中第一个只出现一次的字符
【思路】

class Solution {    
    
    Map<Character, Integer> count = new HashMap<>();
    Queue<Character> q = new LinkedList<>();
    
    //Insert one char from stringstream   
    public void insert(char ch){
        
        q.offer(ch);
        //个数加一
        if( !count.containsKey(ch) ) count.put(ch, 1);
        else count.put(ch, count.get(ch) + 1);
    }
    //return the first appearence once char in current stringstream
    public char firstAppearingOnce(){
        if( !q.isEmpty() &&  count.get( q.peek() ) == 1 ) return q.peek();
        
        while( !q.isEmpty() && count.get(q.peek() ) > 1 ) q.poll();
        return q.isEmpty() ? '#' :q.peek();
        
    }
}