From 4f95b48387c083cdb08f08b48289c78497813789 Mon Sep 17 00:00:00 2001
From: Thushara Samaraweera <thusharadasun204@gmail.com>
Date: Thu, 21 Oct 2021 05:02:09 +0530
Subject: [PATCH] add dequeue in c

---
 Data Structures/Dequeue/dequeue.c | 180 ++++++++++++++++++++++++++++++
 1 file changed, 180 insertions(+)
 create mode 100644 Data Structures/Dequeue/dequeue.c

diff --git a/Data Structures/Dequeue/dequeue.c b/Data Structures/Dequeue/dequeue.c
new file mode 100644
index 0000000..289897f
--- /dev/null
+++ b/Data Structures/Dequeue/dequeue.c	
@@ -0,0 +1,180 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+//self referencing structure with one data element
+struct node{
+    int data;
+    struct node *next, *perv;
+};
+
+// Aliasing for easier referencing
+typedef struct node node;
+
+/*-------------------------------------- Dequeue Functions -------------------------------------- */
+/** Ideally these should go in a seperate Header file (ie. dequeue.h) along with the self referencing structure
+ * 
+ * Note : Dequeue is a ADT which is also a derived DS from LinkedList
+ * 
+ * Dequeue Functions
+ * Create Node       : create
+ * Insert to front   : insertFront (append to the front of Dequeue)
+ * Insert to end     : insertRear (append to the end of Dequeue)
+ * Delete from front : deleteFront (remove the first node of the Dequeue)
+ * Delete from end   : deleteRear (remove the last node of the Dequeue)
+ * Peek from front   : peekFront(views the first element in the Dequeue)
+ * Peek from end     : peekFront(views the last element in the Dequeue)
+ * check emptiness   : IsEmpty(if it is empty, then return 1)
+ * Display List      : display
+ * 
+ */
+
+// create a dequeue 
+typedef struct deqeue{
+    int count;
+    node* front;
+    node* rear;
+}deqeue;
+
+// Creates a Node in Heap and returns a pointer
+
+void create(deqeue* dq){
+    dq->count = 0;
+    dq->front = NULL;
+    dq->rear = NULL;
+}
+
+// check emptiness
+int IsEmpty(deqeue* dq){
+    if(dq->front==NULL && dq->rear==NULL)
+        return 1;
+    else
+        return 0;
+}
+
+// appends a node to the front of the Dequeue
+void insertFront(deqeue* dq, int data){
+    node* np = (node*)malloc(sizeof(node));
+    if(np==NULL)
+        printf("memory is not enoungh...\n");
+    else{
+        dq->count++;
+        np->data = data;
+        np->perv = NULL;
+        if(IsEmpty(dq)){
+            np->next = NULL;
+            dq->front = np;
+            dq->rear = np;
+        }
+        else{
+            np->next = dq->front;
+            dq->front->perv = np;
+            dq->front = np;
+        }
+    }
+}
+
+// appends a node to the end of the Dequeue
+void insertRear(deqeue* dq, int data){
+    node* np = (node*)malloc(sizeof(node));
+    if(np==NULL)
+        printf("memory is not enoungh...\n");
+    else{
+        dq->count++;
+        np->data = data;
+        np->next = NULL;
+        if(IsEmpty(dq)){
+            np->perv = NULL;
+            dq->front = np;
+            dq->rear = np;
+        }
+        else{
+            np->perv = dq->rear;
+            dq->rear->next = np;
+            dq->rear = np;
+        }
+    }
+}
+
+// removes the first element in the dequeue
+void deleteFront(deqeue* dq){
+    if(IsEmpty(dq))
+        printf("deqeue is empty...\n");
+    else{
+        node* temp = dq->front;          // address of node that to be deleted
+        dq->front = dq->front->next;
+        if(dq->front==NULL)              // if deque has one element
+            dq->rear=NULL;
+        else{
+            dq->front->perv = NULL;
+        }
+        free(temp);
+    }
+}
+
+// removes the last element in the dequeue
+void deleteRear(deqeue* dq){
+    if(IsEmpty(dq))
+        printf("deqeue is empty...\n");
+    else{
+        node* temp = dq->rear;
+        dq->rear = dq->rear->perv;
+        if(dq->rear==NULL)
+            dq->front=NULL;
+        else{
+            dq->rear->next = NULL;
+        }
+        free(temp);
+    }
+}
+
+//Takes a peek at the first element in the dequeue
+void peekFront(deqeue* dq){
+    if(IsEmpty(dq))
+        printf("deqeue is empty...\n");
+    else{
+      printf("first element is %d\n", dq->front->data);
+    }
+}
+
+//Takes a peek at the last element in the dequeue
+void peekRear(deqeue* dq){
+  if(IsEmpty(dq))
+    printf("deqeue is empty");
+  else{
+    printf("last eleement is %d\n", dq->rear->data);
+  }
+}
+
+// Prints all the elements in the Dequeue
+void display(deqeue* dq){
+    if(IsEmpty(dq))
+        printf("deqeue is empty...\n");
+    else{
+        node* temp = dq->front;
+        while(temp!=NULL){
+            printf("%d ", temp->data);
+            temp = temp->next;
+        }
+        printf("\n");
+    }
+}
+
+/* --------------------------------- End of Dequeue Functions ----------------------------------- */
+
+
+int main(){
+  deqeue dq;                 // create deqeue
+  create(&dq);
+  insertFront(&dq, 1);
+  insertFront(&dq, 2);
+  display(&dq);
+  peekFront(&dq);
+  insertRear(&dq, 44);
+  peekRear(&dq);
+  display(&dq);
+  deleteRear(&dq);
+  display(&dq);
+
+
+  return 0;
+}
\ No newline at end of file