From 9ca6b1b2a958085f206bb33a4f0f02ff4a0fdafd Mon Sep 17 00:00:00 2001
From: Nihhaar Saini <msnrk2006@hmail.com>
Date: Thu, 23 Oct 2025 13:24:31 +0530
Subject: [PATCH 1/3] Add doubly linked list implementation in C

---
 data_structures/doubly_linked_list.c | 32 ++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 data_structures/doubly_linked_list.c

diff --git a/data_structures/doubly_linked_list.c b/data_structures/doubly_linked_list.c
new file mode 100644
index 0000000000..62e73604dd
--- /dev/null
+++ b/data_structures/doubly_linked_list.c
@@ -0,0 +1,32 @@
+void ins_pos() {
+    int pos;
+    printf("\nEnter the position where the node should be inserted: ");
+    scanf("%d", &pos);
+
+    if (pos < 1 || pos > count() + 1) {
+        printf("\nInvalid position!\n");
+        return;
+    }
+
+    if (pos == 1) {
+        ins_beg();
+        return;
+    }
+
+    struct node *newnode = create_node();  // <<< ADD THIS LINE
+
+    temp = head;
+    for (int i = 1; i < pos - 1; i++) {
+        temp = temp->next;
+    }
+
+    newnode->next = temp->next;
+    newnode->prev = temp;
+
+    if (temp->next != NULL) {
+        temp->next->prev = newnode;
+    }
+
+    temp->next = newnode;
+    printf("\n%d is inserted at position %d\n", newnode->data, pos);
+}

From 6cd7e7ecfbdb2bbb24a54a0c14bc9c4bea5d8450 Mon Sep 17 00:00:00 2001
From: Nihhaar Saini <msnrk2006@hmail.com>
Date: Thu, 23 Oct 2025 13:29:06 +0530
Subject: [PATCH 2/3] Circular linked list implementation in C

---
 data_structures/circular_linked_list.c | 222 +++++++++++++++++++++++++
 1 file changed, 222 insertions(+)
 create mode 100644 data_structures/circular_linked_list.c

diff --git a/data_structures/circular_linked_list.c b/data_structures/circular_linked_list.c
new file mode 100644
index 0000000000..07dfa70ec8
--- /dev/null
+++ b/data_structures/circular_linked_list.c
@@ -0,0 +1,222 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+struct node {
+    int data;
+    struct node* next;
+} *head = NULL, *temp = NULL, *newnode = NULL;
+
+// Create a new node
+struct node* create_node() {
+    newnode = (struct node*)malloc(sizeof(struct node));
+    printf("\nEnter the data: ");
+    scanf("%d", &newnode->data);
+    newnode->next = NULL;
+    return newnode;
+}
+
+// Count nodes in the circular linked list
+int count() {
+    int cnt = 0;
+    if (head == NULL) return 0;
+
+    temp = head;
+    do {
+        cnt++;
+        temp = temp->next;
+    } while (temp != head);
+
+    return cnt;
+}
+
+// Insert at beginning
+void ins_begin() {
+    newnode = create_node();
+    if (head == NULL) {
+        head = newnode;
+        newnode->next = head;
+    } else {
+        temp = head;
+        while (temp->next != head) temp = temp->next;
+        newnode->next = head;
+        head = newnode;
+        temp->next = head;
+    }
+    printf("\n%d is inserted at beginning\n", newnode->data);
+}
+
+// Insert at given position
+void ins_pos(int pos) {
+    if (pos < 1 || pos > count() + 1) {
+        printf("\nInvalid position\n");
+        return;
+    }
+
+    if (pos == 1) {
+        ins_begin();
+        return;
+    }
+
+    newnode = create_node();
+    temp = head;
+    for (int i = 1; i < pos - 1; i++) temp = temp->next;
+
+    newnode->next = temp->next;
+    temp->next = newnode;
+    printf("\n%d is inserted at position %d\n", newnode->data, pos);
+}
+
+// Insert at end
+void ins_end() {
+    newnode = create_node();
+    if (head == NULL) {
+        head = newnode;
+        newnode->next = head;
+    } else {
+        temp = head;
+        while (temp->next != head) temp = temp->next;
+        temp->next = newnode;
+        newnode->next = head;
+    }
+    printf("\n%d is inserted at end\n", newnode->data);
+}
+
+// Delete from beginning
+void del_beg() {
+    if (head == NULL) {
+        printf("\nEmpty list\n");
+        return;
+    }
+
+    struct node* to_delete = head;
+    if (head->next == head) {
+        printf("\n%d is deleted\n", head->data);
+        free(head);
+        head = NULL;
+        return;
+    }
+
+    temp = head;
+    while (temp->next != head) temp = temp->next;
+    head = head->next;
+    temp->next = head;
+
+    printf("\n%d is deleted\n", to_delete->data);
+    free(to_delete);
+}
+
+// Delete from a position
+void del_pos(int pos) {
+    if (head == NULL) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    int total = count();
+    if (pos < 1 || pos > total) {
+        printf("\nInvalid position\n");
+        return;
+    }
+
+    if (pos == 1) {
+        del_beg();
+        return;
+    }
+
+    temp = head;
+    for (int i = 1; i < pos - 1; i++) temp = temp->next;
+
+    struct node* to_delete = temp->next;
+    temp->next = to_delete->next;
+
+    printf("\n%d is deleted\n", to_delete->data);
+    free(to_delete);
+}
+
+// Delete from end
+void del_end() {
+    if (head == NULL) {
+        printf("\nEmpty list\n");
+        return;
+    }
+
+    if (head->next == head) {
+        printf("\n%d is deleted\n", head->data);
+        free(head);
+        head = NULL;
+        return;
+    }
+
+    temp = head;
+    while (temp->next->next != head) temp = temp->next;
+
+    struct node* to_delete = temp->next;
+    temp->next = head;
+
+    printf("\n%d is deleted\n", to_delete->data);
+    free(to_delete);
+}
+
+// Display the list
+void display() {
+    if (head == NULL) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    temp = head;
+    do {
+        printf("%d -> ", temp->data);
+        temp = temp->next;
+    } while (temp != head);
+    printf("(head)\n");
+}
+
+// Main menu
+int main() {
+    int n;
+    while (1) {
+        printf("\nSELECT OPERATION\n");
+        printf("1. Insertion\n2. Deletion\n3. Display\n4. Exit\nEnter your choice: ");
+        scanf("%d", &n);
+
+        switch (n) {
+            case 1: {
+                int x, pos;
+                printf("SELECT INSERTION TYPE:\n1. Insert at beginning\n2. Insert at position\n3. Insert at end\nEnter your choice: ");
+                scanf("%d", &x);
+
+                switch (x) {
+                    case 1: ins_begin(); break;
+                    case 2: 
+                        printf("Enter the position to insert node: ");
+                        scanf("%d", &pos);
+                        ins_pos(pos);
+                        break;
+                    case 3: ins_end(); break;
+                    default: printf("\nInvalid choice for insertion!\n");
+                }
+                break;
+            }
+            case 2: {
+                int z, pos;
+                printf("SELECT DELETION TYPE:\n1. Delete from beginning\n2. Delete from position\n3. Delete from end\nEnter your choice: ");
+                scanf("%d", &z);
+
+                switch (z) {
+                    case 1: del_beg(); break;
+                    case 2: 
+                        printf("Enter the position to delete node: ");
+                        scanf("%d", &pos);
+                        del_pos(pos);
+                        break;
+                    case 3: del_end(); break;
+                    default: printf("\nInvalid choice for deletion!\n");
+                }
+                break;
+            }
+            case 3: display(); break;
+            case 4: printf("\nExiting\n"); exit(0);
+            default: printf("\nInvalid choice\n");
+        }
+    }
+    return 0;
+}

From 91806b757182a46fe711309cdfcb0698d8b65b32 Mon Sep 17 00:00:00 2001
From: Nihhaar Saini <msnrk2006@hmail.com>
Date: Thu, 23 Oct 2025 13:39:44 +0530
Subject: [PATCH 3/3] Add linked list with sorting and utility functions in C

---
 data_structures/sorting_linked_list.c | 307 ++++++++++++++++++++++++++
 1 file changed, 307 insertions(+)
 create mode 100644 data_structures/sorting_linked_list.c

diff --git a/data_structures/sorting_linked_list.c b/data_structures/sorting_linked_list.c
new file mode 100644
index 0000000000..94722ba03b
--- /dev/null
+++ b/data_structures/sorting_linked_list.c
@@ -0,0 +1,307 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+struct node {
+    int data;
+    struct node* next;
+} *head = NULL, *p = NULL, *q = NULL;
+
+// Check if list is empty
+bool is_empty() {
+    return (head == NULL);
+}
+
+// Count nodes in the list
+int count() {
+    int length = 0;
+    if (is_empty()) return 0;
+
+    p = head;
+    while (p != NULL) {
+        length++;
+        p = p->next;
+    }
+    return length;
+}
+
+// Create a new node
+struct node* create_node() {
+    struct node* newnode = (struct node*)malloc(sizeof(struct node));
+    printf("\nEnter the data: ");
+    scanf("%d", &newnode->data);
+    newnode->next = NULL;
+    return newnode;
+}
+
+// Insert at beginning
+void ins_beg() {
+    struct node* newnode = create_node();
+    if (is_empty()) {
+        head = newnode;
+    } else {
+        newnode->next = head;
+        head = newnode;
+    }
+    printf("\n%d is inserted at beginning\n", newnode->data);
+}
+
+// Insert at position
+void ins_pos(int po) {
+    if (po < 1 || po > count() + 1) {
+        printf("\nInvalid position!\n");
+        return;
+    }
+
+    if (po == 1) {
+        ins_beg();
+        return;
+    }
+
+    struct node* newnode = create_node();
+    p = head;
+    for (int i = 1; i < po - 1; i++) p = p->next;
+
+    newnode->next = p->next;
+    p->next = newnode;
+
+    printf("\n%d is inserted at position %d\n", newnode->data, po);
+}
+
+// Insert at end
+void ins_end() {
+    struct node* newnode = create_node();
+    if (is_empty()) {
+        head = newnode;
+    } else {
+        p = head;
+        while (p->next != NULL) p = p->next;
+        p->next = newnode;
+    }
+    printf("\n%d is inserted at end\n", newnode->data);
+}
+
+// Delete from beginning
+void del_begin() {
+    if (is_empty()) {
+        printf("\nEmpty list. Deletion not possible.\n");
+        return;
+    }
+    p = head;
+    head = p->next;
+    printf("\n%d is deleted\n", p->data);
+    free(p);
+}
+
+// Delete from end
+void del_end() {
+    if (is_empty()) {
+        printf("\nEmpty list. Deletion not possible.\n");
+        return;
+    }
+    if (head->next == NULL) {
+        printf("\n%d is deleted\n", head->data);
+        free(head);
+        head = NULL;
+        return;
+    }
+    p = head;
+    while (p->next != NULL) {
+        q = p;
+        p = p->next;
+    }
+    printf("\n%d is deleted\n", p->data);
+    free(p);
+    q->next = NULL;
+}
+
+// Delete from position
+void del_pos(int pos) {
+    if (pos < 1 || pos > count()) {
+        printf("\nInvalid position!\n");
+        return;
+    }
+    if (pos == 1) {
+        del_begin();
+        return;
+    }
+
+    p = head;
+    for (int i = 1; i < pos; i++) {
+        q = p;
+        p = p->next;
+    }
+    q->next = p->next;
+    printf("\n%d is deleted\n", p->data);
+    free(p);
+}
+
+// Display the list
+void display() {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    p = head;
+    while (p != NULL) {
+        printf("%d -> ", p->data);
+        p = p->next;
+    }
+    printf("NULL\n");
+}
+
+// Find maximum element
+void max() {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    p = head;
+    int m = p->data;
+    while (p != NULL) {
+        if (p->data > m) m = p->data;
+        p = p->next;
+    }
+    printf("\n%d is the maximum element\n", m);
+}
+
+// Find minimum element
+void min() {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    p = head;
+    int m = p->data;
+    while (p != NULL) {
+        if (p->data < m) m = p->data;
+        p = p->next;
+    }
+    printf("\n%d is the minimum element\n", m);
+}
+
+// Sort the linked list (Bubble Sort)
+void sort() {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+
+    int size = count();
+    int temp;
+    for (int i = 0; i < size - 1; i++) {
+        p = head;
+        for (int j = 0; j < size - i - 1; j++) {
+            if (p->data > p->next->data) {
+                temp = p->data;
+                p->data = p->next->data;
+                p->next->data = temp;
+            }
+            p = p->next;
+        }
+    }
+    printf("\nSorted list:\n");
+    display();
+}
+
+// Search for an element
+void search(int key) {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    p = head;
+    int pos = 0;
+    bool found = false;
+    while (p != NULL) {
+        pos++;
+        if (p->data == key) {
+            found = true;
+            break;
+        }
+        p = p->next;
+    }
+    if (found)
+        printf("\nElement found at position %d\n", pos);
+    else
+        printf("\nElement not found\n");
+}
+
+// Reverse the list
+void reverse_list() {
+    if (is_empty()) {
+        printf("\nEmpty list\n");
+        return;
+    }
+    struct node *current = head, *prev = NULL, *next = NULL;
+    while (current != NULL) {
+        next = current->next;
+        current->next = prev;
+        prev = current;
+        current = next;
+    }
+    head = prev;
+    printf("\nReversed list:\n");
+    display();
+}
+
+// Main menu
+int main() {
+    int n;
+    while (1) {
+        printf("\nSELECT OPERATION\n");
+        printf("1. Insertion\n2. Deletion\n3. Display\n4. Maximum\n5. Minimum\n6. Sort\n7. Length\n8. Search\n9. Reverse the list\n10. Exit\nEnter your choice: ");
+        scanf("%d", &n);
+
+        switch (n) {
+            case 1: {
+                int x, pos;
+                printf("SELECT INSERTION TYPE:\n1. Insert at beginning\n2. Insert at position\n3. Insert at end\nEnter your choice: ");
+                scanf("%d", &x);
+                switch (x) {
+                    case 1: ins_beg(); break;
+                    case 2:
+                        printf("Enter the position to insert node: ");
+                        scanf("%d", &pos);
+                        ins_pos(pos);
+                        break;
+                    case 3: ins_end(); break;
+                    default: printf("\nInvalid choice for insertion!\n");
+                }
+                break;
+            }
+            case 2: {
+                int z, pos;
+                printf("SELECT DELETION TYPE:\n1. Delete from beginning\n2. Delete from position\n3. Delete from end\nEnter your choice: ");
+                scanf("%d", &z);
+                switch (z) {
+                    case 1: del_begin(); break;
+                    case 2:
+                        printf("Enter the position to delete node: ");
+                        scanf("%d", &pos);
+                        del_pos(pos);
+                        break;
+                    case 3: del_end(); break;
+                    default: printf("\nInvalid choice for deletion!\n");
+                }
+                break;
+            }
+            case 3: display(); break;
+            case 4: max(); break;
+            case 5: min(); break;
+            case 6: sort(); break;
+            case 7: printf("\nNumber of nodes: %d\n", count()); break;
+            case 8: {
+                int key;
+                printf("\nEnter key element: ");
+                scanf("%d", &key);
+                search(key);
+                break;
+            }
+            case 9: reverse_list(); break;
+            case 10: printf("\nExiting\n"); exit(0);
+            default: printf("\nInvalid choice\n");
+        }
+    }
+    return 0;
+}