implement a queue with 2 stacks : done

Author: rampatra

src/com/hackerrank/tutorials/ctci/QueuesWithTwoStacks.java

@@ -0,0 +1,56 @@
+package com.hackerrank.tutorials.ctci;
+
+import java.util.Scanner;
+import java.util.Stack;
+
+/**
+ * Question: https://www.hackerrank.com/challenges/ctci-queue-using-two-stacks
+ * Level: Medium
+ *
+ * @author ramswaroop
+ * @version 07/10/2016
+ */
+public class QueuesWithTwoStacks {
+
+    public static class MyQueue<T> {
+        Stack<T> stackNewestOnTop = new Stack<T>();
+        Stack<T> stackOldestOnTop = new Stack<T>();
+
+        public void enqueue(T value) { // Push onto newest stack
+            stackNewestOnTop.push(value);
+        }
+
+        public T peek() {
+            return stackOldestOnTop.isEmpty() ? stackNewestOnTop.firstElement() : stackOldestOnTop.peek();
+        }
+
+        public T dequeue() {
+            if (stackOldestOnTop.isEmpty()) {
+                while (!stackNewestOnTop.isEmpty()) {
+                    stackOldestOnTop.push(stackNewestOnTop.pop());
+                }
+            }
+            return stackOldestOnTop.pop();
+        }
+    }
+
+
+    public static void main(String[] args) {
+        MyQueue<Integer> queue = new MyQueue<>();
+
+        Scanner scan = new Scanner(System.in);
+        int n = scan.nextInt();
+
+        for (int i = 0; i < n; i++) {
+            int operation = scan.nextInt();
+            if (operation == 1) { // enqueue
+                queue.enqueue(scan.nextInt());
+            } else if (operation == 2) { // dequeue
+                queue.dequeue();
+            } else if (operation == 3) { // print/peek
+                System.out.println(queue.peek());
+            }
+        }
+        scan.close();
+    }
+}