From e173343ae5ab96fe0736eeeae7d0d0c5de111c28 Mon Sep 17 00:00:00 2001
From: DinkyRajpoot56 <dinkyrajpoot6@gamil.com>
Date: Sun, 10 Nov 2024 09:15:49 +0530
Subject: [PATCH] Added Circular Queue using Two Stacks

---
 .../CircularQueueUsingTwoStacks.c             | 147 ++++++++++++++++++
 Queue/CircularQueueUsingTwoStacks/README.md   |  31 ++++
 2 files changed, 178 insertions(+)
 create mode 100644 Queue/CircularQueueUsingTwoStacks/CircularQueueUsingTwoStacks.c
 create mode 100644 Queue/CircularQueueUsingTwoStacks/README.md

diff --git a/Queue/CircularQueueUsingTwoStacks/CircularQueueUsingTwoStacks.c b/Queue/CircularQueueUsingTwoStacks/CircularQueueUsingTwoStacks.c
new file mode 100644
index 00000000..a083aebf
--- /dev/null
+++ b/Queue/CircularQueueUsingTwoStacks/CircularQueueUsingTwoStacks.c
@@ -0,0 +1,147 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX 100
+
+typedef struct
+{
+    int arr[MAX];
+    int top;
+} Stack;
+
+// Function to initialize the stack
+void initStack(Stack *stack)
+{
+    stack->top = -1;
+}
+
+// Function to check if the stack is empty
+int isEmpty(Stack *stack)
+{
+    return stack->top == -1;
+}
+
+// Function to check if the stack is full
+int isFull(Stack *stack)
+{
+    return stack->top == MAX - 1;
+}
+
+// Function to push an element onto the stack
+void push(Stack *stack, int value)
+{
+    if (isFull(stack))
+    {
+        printf("Stack overflow, cannot push %d\n", value);
+        return;
+    }
+    stack->arr[++stack->top] = value;
+}
+
+// Function to pop an element from the stack
+int pop(Stack *stack)
+{
+    if (isEmpty(stack))
+    {
+        printf("Stack underflow, cannot pop\n");
+        return -1;
+    }
+    return stack->arr[stack->top--];
+}
+
+// Function to implement a circular queue using two stacks
+typedef struct
+{
+    Stack stack1;
+    Stack stack2;
+} CircularQueue;
+
+// Function to initialize the circular queue
+void initQueue(CircularQueue *queue)
+{
+    initStack(&queue->stack1);
+    initStack(&queue->stack2);
+}
+
+// Function to enqueue an element into the queue
+void enqueue(CircularQueue *queue, int value)
+{
+    push(&queue->stack1, value);
+}
+
+// Function to dequeue an element from the queue
+int dequeue(CircularQueue *queue)
+{
+    if (isEmpty(&queue->stack2))
+    {
+        // Transfer all elements from stack1 to stack2
+        while (!isEmpty(&queue->stack1))
+        {
+            int temp = pop(&queue->stack1);
+            push(&queue->stack2, temp);
+        }
+    }
+
+    if (isEmpty(&queue->stack2))
+    {
+        printf("Queue is empty, cannot dequeue\n");
+        return -1;
+    }
+
+    return pop(&queue->stack2);
+}
+
+// Function to display the elements of the queue
+void displayQueue(CircularQueue *queue)
+{
+    if (isEmpty(&queue->stack1) && isEmpty(&queue->stack2))
+    {
+        printf("Queue is empty\n");
+        return;
+    }
+
+    // Print elements from stack2 (front of the queue)
+    for (int i = queue->stack2.top; i >= 0; i--)
+    {
+        printf("%d ", queue->stack2.arr[i]);
+    }
+
+    // Print elements from stack1 (end of the queue)
+    for (int i = 0; i <= queue->stack1.top; i++)
+    {
+        printf("%d ", queue->stack1.arr[i]);
+    }
+    printf("\n");
+}
+
+int main()
+{
+    CircularQueue queue;
+    initQueue(&queue);
+
+    // Enqueue elements
+    enqueue(&queue, 10);
+    enqueue(&queue, 20);
+    enqueue(&queue, 30);
+
+    // Display queue
+    printf("Queue after enqueuing 10, 20, 30: ");
+    displayQueue(&queue);
+
+    // Dequeue an element
+    printf("Dequeued element: %d\n", dequeue(&queue));
+
+    // Display queue after dequeue
+    printf("Queue after dequeue: ");
+    displayQueue(&queue);
+
+    // Enqueue more elements
+    enqueue(&queue, 40);
+    enqueue(&queue, 50);
+
+    // Display final state of the queue
+    printf("Queue after enqueuing 40, 50: ");
+    displayQueue(&queue);
+
+    return 0;
+}
diff --git a/Queue/CircularQueueUsingTwoStacks/README.md b/Queue/CircularQueueUsingTwoStacks/README.md
new file mode 100644
index 00000000..1bbfe9c1
--- /dev/null
+++ b/Queue/CircularQueueUsingTwoStacks/README.md
@@ -0,0 +1,31 @@
+# Explanation
+
+Two Stacks (stack1 and stack2): stack1 is used for enqueue operations, while stack2 is used for dequeue operations.
+Enqueue Operation: Pushes the element onto stack1.
+Dequeue Operation: If stack2 is empty, all elements from stack1 are transferred to stack2, reversing their order to maintain the FIFO property. The top element of stack2 is then popped to simulate dequeue.
+Display Operation: Prints elements in stack2 from top to bottom (front of the queue) followed by stack1 from bottom to top (end of the queue).
+
+# Complexity
+
+Time Complexity:
+Enqueue:
+𝑂
+(
+1
+)
+O(1)
+Dequeue:
+𝑂
+(
+𝑛
+)
+O(n) in the worst case (when transferring elements between stacks)
+Space Complexity:
+𝑂
+(
+𝑛
+)
+O(n) where
+𝑛
+n is the total number of elements in the queue.
+This approach ensures that the queue behaves like a circular queue when combined with proper logic for handling full and empty cases.