Merge pull request #1757 from akgmage/dev

add stack using queue in java

Author: akgmage

Stacks/stack_using_queue.java

@@ -0,0 +1,79 @@
+// stack using queue
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class StackUsingQueues {
+    private Queue<Integer> primaryQueue;
+    private Queue<Integer> tempQueue;
+
+    public StackUsingQueues() {
+        primaryQueue = new LinkedList<>();
+        tempQueue = new LinkedList<>();
+    }
+
+    public void push(int value) {
+        // Add the element to the primary queue
+        primaryQueue.offer(value);
+    }
+
+    public int pop() {
+        if (isEmpty()) {
+            throw new IllegalStateException("Stack is empty.");
+        }
+
+        // Move elements from the primary queue to the temporary queue except the last one
+        while (primaryQueue.size() > 1) {
+            tempQueue.offer(primaryQueue.poll());
+        }
+
+        // Get the last element from the primary queue (top of the stack)
+        int topElement = primaryQueue.poll();
+
+        // Swap the primary and temporary queues
+        Queue<Integer> swap = primaryQueue;
+        primaryQueue = tempQueue;
+        tempQueue = swap;
+
+        return topElement;
+    }
+
+    public int top() {
+        if (isEmpty()) {
+            throw new IllegalStateException("Stack is empty.");
+        }
+
+        int topElement = pop();
+
+        // Add the top element back to the stack
+        push(topElement);
+
+        return topElement;
+    }
+
+    public boolean isEmpty() {
+        return primaryQueue.isEmpty();
+    }
+
+    public static void main(String[] args) {
+        StackUsingQueues stack = new StackUsingQueues();
+
+        // Push elements onto the stack
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+
+        // Pop elements from the stack
+        System.out.println(stack.pop()); // Output: 3
+        System.out.println(stack.pop()); // Output: 2
+
+        // Push more elements
+        stack.push(4);
+        stack.push(5);
+
+        // Peek at the top element
+        System.out.println(stack.top()); // Output: 5
+
+        // Check if the stack is empty
+        System.out.println(stack.isEmpty()); // Output: false
+    }
+}