栈和队列的实现

用栈实现队列

• • 1.分析
  • 2.代码

1.分析

2.代码

class MyQueue {
      private Stack<Integer> s1;
      private Stack<Integer> s2;
    public MyQueue() {
      s1 = new Stack<>();
      s2 = new Stack<>();
    }
    
    public void push(int x) {
        s1.push(x);
    }
    
    public int pop() {
        if(empty()){
            return -1;
        }
        if(s2.empty()){
            while(!s1.empty()){
                s2.push(s1.pop());
            }
        }
       return s2.pop();
    }
    
    public int peek() {
         if(empty()){
            return -1;
        }
        if(s2.empty()){
            while(!s1.empty()){
                s2.push(s1.pop());
            }
        }
        return s2.peek();
    }
    
    public boolean empty() {
     return s1.empty()&&s2.empty();
    }
}

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.empty();
 */