From 8689140f692592fefb2afcba3d903d0b102078ad Mon Sep 17 00:00:00 2001
From: Wander_Lust <hvmanoj2@gmail.com>
Date: Thu, 22 Jan 2026 17:02:44 +0530
Subject: [PATCH] Add DS lab linked list, stack and queue implementations

---
 doublyLL.c | 126 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 queueLL.c  |  98 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 224 insertions(+)
 create mode 100644 doublyLL.c
 create mode 100644 queueLL.c

diff --git a/doublyLL.c b/doublyLL.c
new file mode 100644
index 0000000..8863e59
--- /dev/null
+++ b/doublyLL.c
@@ -0,0 +1,126 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+
+typedef struct node {
+    int data;
+    struct node *prev;
+    struct node *next;
+} NODE;
+
+
+NODE *head = NULL;
+
+
+void insert_front(int value) {
+    NODE *newNode = (NODE *)malloc(sizeof(NODE));
+
+    if (newNode == NULL) {
+        printf("Memory allocation failed\n");
+        return;
+    }
+
+    newNode->data = value;
+    newNode->prev = NULL;
+    newNode->next = head;
+
+    if (head != NULL) {
+        head->prev = newNode;
+    }
+
+    head = newNode;
+    printf("Inserted %d\n", value);
+}
+
+
+void delete_value(int value) {
+    NODE *temp = head;
+
+    if (head == NULL) {
+        printf("List is empty\n");
+        return;
+    }
+
+    while (temp != NULL) {
+        if (temp->data == value) {
+
+            
+            if (temp->prev == NULL) {
+                head = temp->next;
+                if (head != NULL)
+                    head->prev = NULL;
+            }
+        
+            else {
+                temp->prev->next = temp->next;
+                if (temp->next != NULL)
+                    temp->next->prev = temp->prev;
+            }
+
+            free(temp);
+            printf("Deleted %d\n", value);
+            return;
+        }
+        temp = temp->next;
+    }
+
+    printf("Value not found\n");
+}
+
+void display() {
+    NODE *temp = head;
+
+    if (head == NULL) {
+        printf("List is empty\n");
+        return;
+    }
+
+    printf("List: ");
+    while (temp != NULL) {
+        printf("%d <-> ", temp->data);
+        temp = temp->next;
+    }
+    printf("NULL\n");
+}
+
+
+int main() {
+    int choice, value;
+
+    while (1) {
+        printf("\n--- DOUBLY LINKED LIST MENU ---\n");
+        printf("1. Insert at front\n");
+        printf("2. Delete by value\n");
+        printf("3. Display\n");
+        printf("4. Exit\n");
+        printf("Enter choice: ");
+        scanf("%d", &choice);
+
+        switch (choice) {
+
+            case 1:
+                printf("Enter value to insert: ");
+                scanf("%d", &value);
+                insert_front(value);
+                break;
+
+            case 2:
+                printf("Enter value to delete: ");
+                scanf("%d", &value);
+                delete_value(value);
+                break;
+
+            case 3:
+                display();
+                break;
+
+            case 4:
+                printf("Exiting...\n");
+                exit(0);
+
+            default:
+                printf("Invalid choice\n");
+        }
+    }
+}
+
diff --git a/queueLL.c b/queueLL.c
new file mode 100644
index 0000000..ec142cc
--- /dev/null
+++ b/queueLL.c
@@ -0,0 +1,98 @@
+#include<stdio.h>
+#include<stdlib.h>
+
+typedef struct node{
+    int data;
+    struct node* next;
+}Node;
+
+Node* front = NULL;
+Node* rear = NULL;
+
+void enqueue(int value)
+{   
+    Node* newnode = (Node*)malloc(sizeof(Node));
+
+    if(!newnode){
+        fprintf(stderr, "Memory allocation failed\n");
+        exit(1);
+    }
+
+    newnode->data = value;
+    newnode->next = NULL;
+
+    if(front == NULL){
+        rear = front = newnode;
+    }else{
+        rear->next = newnode;
+        rear = newnode;
+    }
+    printf("added %d onto rear\n", value);
+
+
+}
+
+int dequeue(){
+    Node* temp = front;
+    int item;
+    if(front == NULL){
+        printf("stack is empty");
+        return -1;
+    }
+    item = temp->data;
+    front = front->next;
+    free(temp);
+
+    if(front== NULL){
+        rear = NULL;
+    }
+    return item;
+}
+
+void display(){
+    Node* temp = front;
+    if(front == NULL){
+        printf("Stack is empty");
+        return;
+    }
+
+    while(temp!=NULL){
+        printf("%d->",temp->data);
+        temp = temp->next;
+
+    }
+    printf("NULL\n");
+}
+int main(){
+    int choice,value;
+    while(1){
+        printf("\n---queue menu---");
+        printf("\n1. enqueue");
+        printf("\n2. dequeue");
+        printf("\n3. display");
+        printf("\n4. exit");
+        printf("\nEnter your choice: ");
+        scanf("%d", &choice);
+
+        switch(choice){
+            case 1: printf("Enter item to be added: ");
+                    scanf("%d", &value);
+                    enqueue(value);
+                    break;
+            case 2: value = dequeue();
+                    if(value!=-1)
+                    printf("popped %d", value);
+                    break;
+            case 3: display();
+                    break;
+            case 4: printf("exiting\n");
+                    exit(0);
+            default: 
+                    printf("enter valid choice bruh");
+
+
+        }
+
+    }
+    return 0;
+}