Sorted insert in a doubly linked list with head and tail pointers

A Doubly linked list is a linked list that consists of a set of sequentially linked records called nodes. Each node contains two fields that are references to the previous and to the next node in the sequence of nodes.

The task is to create a doubly linked list by inserting nodes such that list remains in ascending order on printing from left to right. Also, we need to maintain two pointers, head (points to first node) and tail (points to last node).

Examples:

Input : 40 50 10 45 90 100 95
Output :10 40 45 50 90 95 100

Input : 30 10 50 43 56 12
Output :10 12 30 43 50 56


Algorithm:
The task can be accomplished as:

  1. If Linked list is empty then make both the left and right pointers point to the node to be inserted and make its previous and next field point to NULL.
  2. If node to be inserted has value less than the value of first node of linked list then connect that node from previous field of first node.
  3. If node to be inserted has value more than the value of last node of linked list then connect that node from next field of last node.
  4. If node to be inserted has value in between the value of first and last node, then check for appropriate position and make connections.
/* C program to insetail nodes in doubly
linked list such that list remains in
ascending order on printing from left
to right */
#include<stdio.h>
#include<stdlib.h>

// A linked list node
struct Node
{
    struct Node *prev;
    int info;
    struct Node *next;
};

// Function to insetail new node
void nodeInsetail(struct Node **head,
                  struct Node **tail,
                  int key)
{

    struct Node *p = new Node;
    p->info = key;
    p->next = NULL;

    // If first node to be insetailed in doubly
    // linked list
    if ((*head) == NULL)
    {
        (*head) = p;
        (*tail) = p;
        (*head)->prev = NULL;
        return;
    }

    // If node to be insetailed has value less
    // than first node
    if ((p->info) < ((*head)->info))
    {
        p->prev = NULL;
        (*head)->prev = p;
        p->next = (*head);
        (*head) = p;
        return;
    }

    // If node to be insetailed has value more
    // than last node
    if ((p->info) > ((*tail)->info))
    {
        p->prev = (*tail);
        (*tail)->next = p;
        (*tail) = p;
        return;
    }

    // Find the node before which we need to
    // insert p.
    temp = (*head)->next;
    while ((temp->info) < (p->info))
        temp = temp->next;

    // Insert new node before temp
    (temp->prev)->next = p;
    p->prev = temp->prev;
    temp->prev = p;
    p->next = temp;
}

// Function to print nodes in from left to right
void printList(struct Node *temp)
{
    while (temp != NULL)
    {
        printf("%d ", temp->info);
        temp = temp->next;
    }
}

// Driver program to test above functions
int main()
{
    struct Node *left = NULL, *right = NULL;
    nodeInsetail(&left, &right, 30);
    nodeInsetail(&left, &right, 50);
    nodeInsetail(&left, &right, 90);
    nodeInsetail(&left, &right, 10);
    nodeInsetail(&left, &right, 40);
    nodeInsetail(&left, &right, 110);
    nodeInsetail(&left, &right, 60);
    nodeInsetail(&left, &right, 95);
    nodeInsetail(&left, &right, 23);

    printf("\nDoubly linked list on printing"
           " from left to right\n");
    printList(left);

    return 0;
}
Output:

Doubly linked list on printing from left to right
10 23 30 40 50 60 90 95 110


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