MyQueue.java

// Time Complexity : O(1)
// Space Complexity : O(n)
// Did this code successfully run on Leetcode : Yes
// Any problem you faced while coding this : No


// Approach:
// Use one stack for push operations and another for pop/peek.
// Transfer elements only when needed to maintain FIFO order.


import java.util.Stack;

class MyQueue {
    Stack<Integer> inputStack;
    Stack<Integer> outputStack;

    public MyQueue() {
        this.inputStack = new Stack<>();
        this.outputStack = new Stack<>();
    }
    
    public void push(int x) {
        inputStack.push(x);
    }
    
    public int pop() {
        if (outputStack.isEmpty()) {
            while (!inputStack.isEmpty()) {
                outputStack.push(inputStack.pop());
            }
        }
        return outputStack.pop();
    }
    
    public int peek() {
        if (outputStack.isEmpty()) {
            while (!inputStack.isEmpty()) {
                outputStack.push(inputStack.pop());
            }
        }
        return outputStack.peek();
    }
    
    public boolean empty() {
        return inputStack.isEmpty() && outputStack.isEmpty();
    }
}