c: queue using stack

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

Author: Ayushd70

c/queueUsingStack.c

@@ -0,0 +1,120 @@
+/* C Program to implement a queue using two stacks */
+#include <stdio.h>
+#include <stdlib.h>
+
+/* structure of a stack node */
+struct sNode
+{
+    int data;
+    struct sNode *next;
+};
+
+/* Function to push an item to stack*/
+void push(struct sNode **top_ref, int new_data);
+
+/* Function to pop an item from stack*/
+int pop(struct sNode **top_ref);
+
+/* structure of queue having two stacks */
+struct queue
+{
+    struct sNode *stack1;
+    struct sNode *stack2;
+};
+
+/* Function to enqueue an item to queue */
+void enQueue(struct queue *q, int x)
+{
+    push(&q->stack1, x);
+}
+
+/* Function to deQueue an item from queue */
+int deQueue(struct queue *q)
+{
+    int x;
+
+    /* If both stacks are empty then error */
+    if (q->stack1 == NULL && q->stack2 == NULL)
+    {
+        printf("Q is empty");
+        getchar();
+        exit(0);
+    }
+
+    /* Move elements from stack1 to stack 2 only if
+       stack2 is empty */
+    if (q->stack2 == NULL)
+    {
+        while (q->stack1 != NULL)
+        {
+            x = pop(&q->stack1);
+            push(&q->stack2, x);
+        }
+    }
+
+    x = pop(&q->stack2);
+    return x;
+}
+
+/* Function to push an item to stack*/
+void push(struct sNode **top_ref, int new_data)
+{
+    /* allocate node */
+    struct sNode *new_node = (struct sNode *)malloc(sizeof(struct sNode));
+    if (new_node == NULL)
+    {
+        printf("Stack overflow \n");
+        getchar();
+        exit(0);
+    }
+
+    /* put in the data */
+    new_node->data = new_data;
+
+    /* link the old list off the new node */
+    new_node->next = (*top_ref);
+
+    /* move the head to point to the new node */
+    (*top_ref) = new_node;
+}
+
+/* Function to pop an item from stack*/
+int pop(struct sNode **top_ref)
+{
+    int res;
+    struct sNode *top;
+
+    /*If stack is empty then error */
+    if (*top_ref == NULL)
+    {
+        printf("Stack underflow \n");
+        getchar();
+        exit(0);
+    }
+    else
+    {
+        top = *top_ref;
+        res = top->data;
+        *top_ref = top->next;
+        free(top);
+        return res;
+    }
+}
+
+int main()
+{
+    /* Create a queue with items 1 2 3*/
+    struct queue *q = (struct queue *)malloc(sizeof(struct queue));
+    q->stack1 = NULL;
+    q->stack2 = NULL;
+    enQueue(q, 1);
+    enQueue(q, 2);
+    enQueue(q, 3);
+
+    /* Dequeue items */
+    printf("%d ", deQueue(q));
+    printf("%d ", deQueue(q));
+    printf("%d ", deQueue(q));
+
+    return 0;
+}