【LeetCode232】 Implement Queue using Stacks★

1.题目描述

2.思路

　　思路简单，这里用一个图来举例说明：

3.java代码

public class MyQueue {

   Stack<Integer> stack1=new Stack<Integer>();
    Stack<Integer> stack2=new Stack<Integer>();
    
    /** Push element x to the back of queue. */
    public void push(int x) {
        stack1.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        if(!stack2.isEmpty())
            return stack2.pop();
        else{
            while(!stack1.empty())
                stack2.push(stack1.pop());
            return stack2.pop();
        }
    }
    
    /** Get the front element. */
    public int peek() {
        if(!stack2.isEmpty())
            return stack2.peek();
        else{
            while(!stack1.empty())
                stack2.push(stack1.pop());
            return stack2.peek();
        }
    }
    
    /** Returns whether the queue is empty. */
    public boolean empty() {
        return stack1.empty()&&stack2.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();
 */