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


// Your code here along with comments explaining your approach

import java.util.Stack;

class MyQueue {

    Stack<Integer> inStack;
    Stack<Integer> outStack;

    public MyQueue() {
        inStack = new Stack<Integer>();
        outStack = new Stack<Integer>();
    }

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

    public int pop() {
        if (empty())
            return -1;

        if (outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
        return outStack.pop();
    }

    public int peek() {
        if (outStack.isEmpty()) {
            while (!inStack.isEmpty()) {
                outStack.push(inStack.pop());
            }
        }
        return outStack.peek();
    }

    public boolean empty() {
        return inStack.isEmpty() && outStack.isEmpty();

    }
}