Solution.java

package implementQueueUsingStacks;

import java.util.Stack;

public class Solution {
    
    class MyQueue {

        private Stack<Integer> in = new Stack<>();
        private Stack<Integer> out = new Stack<>();
    
        /** Initialize your data structure here. */
        public MyQueue() {
            
        }
        
        /** Push element x to the back of queue. */
        public void push(int x) {
            in.push(x);
            
        }
        
        /** Removes the element from in front of queue and returns that element. */
        public int pop() {
            in2out();
            return out.pop();
            
        }
        
        /** Get the front element. */
        public int peek() {
            in2out();
            return out.peek();
        }
        
        /** Returns whether the queue is empty. */
        public boolean empty() {
            return in.isEmpty() && out.isEmpty();
        }
    
        private void in2out() {
            if (out.isEmpty()) {
                while (!in.isEmpty()) {
                    out.push(in.pop());
                }
            }
        }
    }
}