LeetCode-225. 用队列实现栈-Java-easy

题目链接

法一

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */
public class Solution225 {
    private Queue<Integer> q1; //输入队列
    private Queue<Integer> q2; //输出队列

    public Solution225() {
        q1 = new LinkedList<>();
        q2 = new LinkedList<>();
    }

    public void push(int x) {
        q1.offer(x);
        while(!q2.isEmpty()){ // 将q2队列中元素全部转给q1队列
            q1.offer(q2.poll());
        }
        Queue tmp = q1; // 交换q1和q2,使得q1队列没有在push()的时候始终为空队列
        q1 = q2;
        q2 = tmp;
    }

    public int pop() {
        return q2.poll();
    }

    public int top() {
        return q2.peek();
    }

    public boolean empty() {
        return q2.isEmpty();
    }
}

本地测试

        /**
         * 225. 用队列实现栈
         */
        lay.showTitle(225);
        Solution225 sol225 = new Solution225();
        sol225.push(1);
        sol225.push(2);
        System.out.println(sol225.top());
        System.out.println(sol225.pop());
        System.out.println(sol225.empty());