java: queue using stack

Signed-off-by: Ayush Dubey <[email protected]>

Author: Ayushd70

java/queueUsingStack.java

@@ -0,0 +1,75 @@
+/* Java Program to implement a queue using two stacks */
+// Note that Stack class is used for Stack implementation
+
+import java.util.Stack;
+
+public class queueUsingStack {
+    /* class of queue having two stacks */
+    static class Queue {
+        Stack<Integer> stack1;
+        Stack<Integer> stack2;
+    }
+
+    /* Function to push an item to stack */
+    static void push(Stack<Integer> top_ref, int new_data) {
+        // Push the data onto the stack
+        top_ref.push(new_data);
+    }
+
+    /* Function to pop an item from stack */
+    static int pop(Stack<Integer> top_ref) {
+        /* If stack is empty then error */
+        if (top_ref.isEmpty()) {
+            System.out.println("Stack Underflow");
+            System.exit(0);
+        }
+
+        // pop the data from the stack
+        return top_ref.pop();
+    }
+
+    // Function to enqueue an item to the queue
+    static void enQueue(Queue q, int x) {
+        push(q.stack1, x);
+    }
+
+    /* Function to deQueue an item from queue */
+    static int deQueue(Queue q) {
+        int x;
+
+        /* If both stacks are empty then error */
+        if (q.stack1.isEmpty() && q.stack2.isEmpty()) {
+            System.out.println("Q is empty");
+            System.exit(0);
+        }
+
+        /*
+         * Move elements from stack1 to stack 2 only if
+         * stack2 is empty
+         */
+        if (q.stack2.isEmpty()) {
+            while (!q.stack1.isEmpty()) {
+                x = pop(q.stack1);
+                push(q.stack2, x);
+            }
+        }
+        x = pop(q.stack2);
+        return x;
+    }
+
+    /* Driver function to test above functions */
+    public static void main(String args[]) {
+        /* Create a queue with items 1 2 3 */
+        Queue q = new Queue();
+        q.stack1 = new Stack<>();
+        q.stack2 = new Stack<>();
+        enQueue(q, 1);
+        enQueue(q, 2);
+        enQueue(q, 3);
+
+        /* Dequeue items */
+        System.out.print(deQueue(q) + " ");
+        System.out.print(deQueue(q) + " ");
+        System.out.println(deQueue(q) + " ");
+    }
+}