lintcode 40. 用栈实现队列

使用两个栈来回倒腾可以实现队列。

AC代码：

import java.util.Stack;

public class Queue {
    
    private Stack<Integer> stack1;
    private Stack<Integer> stack2;

    public Queue() {
        stack1=new Stack<>();
        stack2=new Stack<>();
    }
    
    public void push(int element) {
        stack1.push(element);
    }

    public int pop() {
        dump(stack1,stack2);
        int res=stack2.pop();
        dump(stack2,stack1);
        return res;
    }

    public int top() {
        dump(stack1,stack2);
        int res=stack2.peek();
        dump(stack2,stack1);
        return res;
    }
    
    private void dump(Stack<Integer> stack1,Stack<Integer> stack2){
        while(!stack1.isEmpty()){
            stack2.push(stack1.pop());
        }
    }
}

题目来源： http://www.lintcode.com/zh-cn/problem/implement-queue-by-two-stacks/