Linked List (2)

Insert an item into a Circular Linked List

int insert_circular(node **head, int data)
{
    node *p1;
    node *new = (node*)malloc(sizeof(node));
    new->value = data;
 
    if (*head == NULL) { 
        *head = new;
        *head->next = *head;   // for circular linked list 
        return new->value;
    } 
 
    p1 = *head;
    while (p1->next != *head) {// find the node before head
        p1 = p1->next;
    }
 
    p1->next = new;            // insert head
    new->next = *head;
    *head = new;
 
    return new->value;
}

Insert an item into a Double Linked List
int insert_double(node** head, int num) 
{
 
        node *p0, *p1, *p2;
    p2 = (node*)malloc(sizeof(node));
    p2 -> data = num;         
    if (*head == null) {
        *head = p2;
        p2->prev = null;
        return num;
    }
    p1 = *head;
    while (p1 != NULL && p1->data > num) {
        p0 = p1;
        p1 = p1->next;
    }
    if (p1 == *head) {    // Special Case!
        p2->next = p1;
        p2->prev = NULL;
        *head = p2;
    }
    else {
        p0->next = p2;
        p2->prev = p0;
        p2->next = p1;
        if (p1 != NULL)
            p1->prev = p2;
    }
 
    return num;
}

Delete an item in a Linked List
Node* Remove(Node *head, int value)
{
    Node *p0, *p1, *temp;
    p1 = head;
 
    while (p1 != NULL && p1->data != value) {
        p0 = p1;
        p1 = p1->next;
    }
 
    if (p1 == NULL) {               // Special Case! can't find
        printf("can't find item\n");
    }
    else if (p1 == head) {       // Special Case! find out at head
        head = head->next;
        free(p1);
    }
    else {                       // otherwise
        p0->next = p1->next;
        free(p1);
    }
 
    return head;
}

Reverse a Linked List: Ex. 1->7->5->3->Null => 3->5->7->1->Null
Node* Reverse(Node* head)
{
    Node *p0, *p1, *temp;
    p0 = NULL;
    p1 = head;
 
    while (p1 != NULL) {// reverse linked list
        temp = p1->next;// you could draw a linked list on paper,
        p1->next = p0;  // to understand why it reverses the list.
        p0 = p1;
        p1 = temp;
    }
 
    return p0;       // if head == NULL, p0 is also NULL
}