代码随想录算法训练营第十天 | 栈与队列part01

题目：

232.用栈实现队列 ，225. 用队列实现栈

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学习内容：

232.用栈实现队列

这道题其实就是用两个栈，stackIn和stackOut来模拟。

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();
    }

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

/**
 * 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();
 */

时间复杂度: push和empty为O(1), pop和peek为O(n)
空间复杂度：O(n)

225. 用队列实现栈

一个队列模拟

class MyStack {
    Deque<Integer> que1;
    public MyStack() {
        que1 = new ArrayDeque<>();
    }
    
    public void push(int x) {
        que1.addLast(x);
    }
    
    public int pop() {
        int size = que1.size();
        size--;
        while (size > 0) {
            que1.addLast(que1.peekFirst());
            que1.pollFirst();
            size--;
        }
        return que1.pollFirst();
    }
    
    public int top() {
        return que1.peekLast();
    }
    
    public boolean empty() {
        return que1.isEmpty();
    }
}

/**
 * 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();
 */

学习时间：

2024.3.15