算法训练营Day10（栈和队列）

232.用栈实现队列 

232. 用栈实现队列 - 力扣（LeetCode）

public class MyQueue {
    //     3 4
    // in
    // out 4 3
    Stack<Integer> in;
    Stack<Integer> out;

    public MyQueue() {
        in = new Stack<>();
        out = new Stack<>();
    }

    public void push(int x) {
        in.push(x);
    }

    public int pop() {
        //先看需不需要补充元素
        dumpOut();
        return out.pop();
    }

    private void dumpOut() {
        //不为空，直接结束方法
        if(!out.isEmpty()) return;
        while(!in.isEmpty()){
            out.push(in.pop());
        }
    }

    public int peek() {
        dumpOut();
        return out.peek();
    }

    public boolean empty() {
        return in.isEmpty()&&out.isEmpty();
    }

}

public class MyStack {
    Queue<Integer> queue;
    public MyStack() {
        queue = new LinkedList<>();
    }

    public void push(int x) {
        queue.offer(x);
    }

    public int pop() {
        rePositon();
        return queue.poll();
    }

    private void rePositon() {
        int size = queue.size();
        size--;
        while (size-->0){
            queue.offer(queue.poll());
        }
    }

    public int top() {
        rePositon();
        int res = queue.poll();
        queue.offer(res);
        return res;
    }

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