代码随想录Day_10|Leetcode.232.225

232.用栈实现队列

import java.util.Stack;

Stack<>();

import java.util.Stack;

//leetcode submit region begin(Prohibit modification and deletion)
class MyQueue {
    Stack<Integer> stackIn;
    Stack<Integer> stackOut;

    public MyQueue() {
        stackIn = new Stack<>();
        stackOut = new Stack<>();
    }

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

    public int pop() {
        dumpstackin();
        return stackOut.pop();
    }

    public int peek() {
        dumpstackin();
        return stackOut.peek();
    }

    public boolean empty() {
        return stackIn.isEmpty() && stackOut.isEmpty();
    }

    private void dumpstackin() {
        if (!stackOut.isEmpty()) return;
        while (!stackIn.isEmpty()) {
            stackOut.push(stackIn.pop());
        }
    }
}

225.用队列实现栈

双端队列Deque

class MyStack {
    Deque<Integer> que1;
    /** Initialize your data structure here. */
    public MyStack() {
        que1 = new ArrayDeque<>();
    }
    
    public void push(int x) {
        que1.addLast(x);
        
    }
    
    public int pop() {
        int size = que1.size();
        size--;
        // 将 que1 导入 que2 ，但留下最后一个值
        while (size-- > 0) {
            que1.addLast(que1.peekFirst());
            que1.pollFirst();
        }

        int res = que1.pollFirst();
        return res;
    }

    /** Get the top element. */
    public int top() {
        return que1.peekLast();
    }

    /** Returns whether the stack is empty. */
    public boolean empty() {
        return que1.isEmpty();
    }
}