leetcode-implement-queue-using-stacks

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题目大意

　　https://leetcode.com/problems/implement-queue-using-stacks

　　利用栈实现一个队列

题目分析

　　使用两个栈，插入时借助辅助栈调整为正确的出队顺序即可。

代码

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public class MyQueue {
    
    Stack<Integer> s1;
    Stack<Integer> s2;
    
    /** Initialize your data structure here. */
    public MyQueue() {
        s1 = new Stack<Integer>();
        s2 = new Stack<Integer>();
    }
    
    /** Push element x to the back of queue. */
    public void push(int x) {
        while (!s1.empty()) {
            s2.push(s1.pop());
        }
        s1.push(x);
        while (!s2.empty()) {
            s1.push(s2.pop());
        }
    }
    
    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        return s1.pop();
    }
    
    /** Get the front element. */
    public int peek() {
        return s1.peek();
    }
    
    /** Returns whether the queue is empty. */
    public boolean empty() {
        return s1.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();
 */