06-Implement-Stack-using-Queues.md

Implement Stack using Queues

Problem Link

https://leetcode.com/problems/implement-stack-using-queues/

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Pattern

• Stack
• Queue
• Design

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Approach

Use a queue and rotate elements on push so the newest element stays at the front.

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Time Complexity

O(n) per push, O(1) per pop/top

Space Complexity

O(n)

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Java Solution

import java.util.*;
class MyStack {
    private Queue<Integer> queue = new LinkedList<>();

    public void push(int x) {
        queue.offer(x);
        for (int i = 0; i < queue.size() - 1; i++) queue.offer(queue.poll());
    }

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

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

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