Given a linked list which is sorted, how will you insert in sorted way

Given a sorted linked list and a value to insert, write a function to insert the value in a sorted way.
Initial Linked List 

Linked List after insertion of 9  

Algorithm: 
Let input linked list is sorted in increasing order. 

1) If Linked list is empty then make the node as
   head and return it.
2) If the value of the node to be inserted is smaller 
   than the value of the head node, then insert the node 
at the start and make it head.
3) In a loop, find the appropriate node after 
   which the input node (let 9) is to be inserted. 
   To find the appropriate node start from the head, 
   keep moving until you reach a node GN (10 in
   the below diagram) who's value is greater than 
   the input node. The node just before GN is the
appropriate node (7).
4) Insert the node (9) after the appropriate node
   (7) found in step 3.

Implementation:

C++

/* Program to insert in a sorted list */
#include <bits/stdc++.h>
using namespace std;

/* Link list node */
class Node {
public:
    int data;
    Node* next;
};

/* function to insert a new_node
in a list. Note that this
function expects a pointer to
head_ref as this can modify the
head of the input linked list
(similar to push())*/
void sortedInsert(Node** head_ref,
                  Node* new_node)
{
    Node* current;
    /* Special case for the head end */
    if (*head_ref == NULL
        || (*head_ref)->data
               >= new_node->data) {
        new_node->next = *head_ref;
        *head_ref = new_node;
    }
    else {
        /* Locate the node before the
 point of insertion */
        current = *head_ref;
        while (current->next != NULL
&& current->next->data
< new_node->data) {
            current = current->next;
        }
        new_node->next = current->next;
        current->next = new_node;
    }
}

/* BELOW FUNCTIONS ARE JUST
UTILITY TO TEST sortedInsert */

/* A utility function to
create a new node */
Node* newNode(int new_data)
{
    /* allocate node */
    Node* new_node = new Node();

    /* put in the data */
    new_node->data = new_data;
    new_node->next = NULL;

    return new_node;
}

/* Function to print linked list */
void printList(Node* head)
{
    Node* temp = head;
    while (temp != NULL) {
        cout << temp->data << " ";
        temp = temp->next;
    }
}

/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    Node* head = NULL;
    Node* new_node = newNode(5);
    sortedInsert(&head, new_node);
    new_node = newNode(10);
    sortedInsert(&head, new_node);
    new_node = newNode(7);
    sortedInsert(&head, new_node);
    new_node = newNode(3);
    sortedInsert(&head, new_node);
    new_node = newNode(1);
    sortedInsert(&head, new_node);
    new_node = newNode(9);
    sortedInsert(&head, new_node);
    cout << "Created Linked List\n";
    printList(head);

    return 0;
}
// This is code is contributed by rathbhupendra

C

/* Program to insert in a sorted list */
#include <stdio.h>
#include <stdlib.h>

/* Link list node */
struct Node {
    int data;
    struct Node* next;
};

/* function to insert a new_node
 in a list. Note that this
  function expects a pointer
to head_ref as this can modify the
  head of the input linked
list (similar to push())*/
void sortedInsert(struct Node** head_ref,
                  struct Node* new_node)
{
    struct Node* current;
    /* Special case for the head end */
    if (*head_ref == NULL
        || (*head_ref)->data
               >= new_node->data) {
        new_node->next = *head_ref;
        *head_ref = new_node;
    }
    else {
        /* Locate the node before
the point of insertion */
        current = *head_ref;
        while (current->next != NULL
               && current->next->data < new_node->data) {
            current = current->next;
        }
        new_node->next = current->next;
        current->next = new_node;
    }
}

/* BELOW FUNCTIONS ARE JUST UTILITY TO TEST sortedInsert */

/* A utility function to create a new node */
struct Node* newNode(int new_data)
{
    /* allocate node */
    struct Node* new_node
= (struct Node*)malloc(
sizeof(struct Node));

    /* put in the data  */
    new_node->data = new_data;
    new_node->next = NULL;

    return new_node;
}

/* Function to print linked list */
void printList(struct Node* head)
{
    struct Node* temp = head;
    while (temp != NULL) {
        printf("%d  ", temp->data);
        temp = temp->next;
    }
}

/* Driver program to test count function*/
int main()
{
    /* Start with the empty list */
    struct Node* head = NULL;
    struct Node* new_node = newNode(5);
    sortedInsert(&head, new_node);
    new_node = newNode(10);
    sortedInsert(&head, new_node);
    new_node = newNode(7);
    sortedInsert(&head, new_node);
    new_node = newNode(3);
    sortedInsert(&head, new_node);
    new_node = newNode(1);
    sortedInsert(&head, new_node);
    new_node = newNode(9);
    sortedInsert(&head, new_node);
    printf("\n Created Linked List\n");
    printList(head);

    return 0;
}

Java

// Java Program to insert in a sorted list
class LinkedList {
    Node head; // head of list

    /* Linked list Node*/
    class Node {
        int data;
        Node next;
        Node(int d)
        {
            data = d;
            next = null;
        }
    }

    /* function to insert a
new_node in a list. */
    void sortedInsert(Node new_node)
    {
        Node current;

        /* Special case for head node */
        if (head == null || head.data
>= new_node.data) {
            new_node.next = head;
            head = new_node;
        }
        else {

            /* Locate the node before point of insertion. */
            current = head;

            while (current.next != null
&& current.next.data < new_node.data) {

              current = current.next;
            }

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    /*Utility functions*/

    /* Function to create a node */
    Node newNode(int data)
    {
        Node x = new Node(data);
        return x;
    }

    /* Function to print linked list */
    void printList()
    {
        Node temp = head;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
    }

    /* Driver function to test above methods */
    public static void main(String args[])
    {
        LinkedList llist = new LinkedList();
        Node new_node;
        new_node = llist.newNode(5);
        llist.sortedInsert(new_node);
        new_node = llist.newNode(10);
        llist.sortedInsert(new_node);
        new_node = llist.newNode(7);
        llist.sortedInsert(new_node);
        new_node = llist.newNode(3);
        llist.sortedInsert(new_node);
        new_node = llist.newNode(1);
        llist.sortedInsert(new_node);
        new_node = llist.newNode(9);
        llist.sortedInsert(new_node);
        System.out.println("Created Linked List");
        llist.printList();
    }
}
/* This code is contributed by Rajat Mishra */

Python

# Python program to insert in a sorted list

# Node class
class Node:

    # Constructor to initialize the node object
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkedList:

    # Function to initialize head
    def __init__(self):
        self.head = None

    def sortedInsert(self, new_node):

        # Special case for the empty linked list
        if self.head is None:
            new_node.next = self.head
            self.head = new_node

        # Special case for head at end
        elif self.head.data >= new_node.data:
            new_node.next = self.head
            self.head = new_node

        else :

            # Locate the node before the point of insertion
            current = self.head
            while(current.next is not None and
                 current.next.data < new_node.data):
                current = current.next

            new_node.next = current.next
            current.next = new_node

    # Function to insert a new node at the beginning
    def push(self, new_data):
        new_node = Node(new_data)
        new_node.next = self.head
        self.head = new_node

    # Utility function to print it the LinkedList
    def printList(self):
        temp = self.head
        while(temp):
            print temp.data,
            temp = temp.next


# Driver program
llist = LinkedList()
new_node = Node(5)
llist.sortedInsert(new_node)
new_node = Node(10)
llist.sortedInsert(new_node)
new_node = Node(7)
llist.sortedInsert(new_node)
new_node = Node(3)
llist.sortedInsert(new_node)
new_node = Node(1)
llist.sortedInsert(new_node)
new_node = Node(9)
llist.sortedInsert(new_node)
print "Create Linked List"
llist.printList()

# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#

// C# Program to insert in a sorted list
using System;

public class LinkedList {
    Node head; // head of list

    /* Linked list Node*/
    class Node {
        public int data;
        public Node next;
        public Node(int d)
        {
            data = d;
            next = null;
        }
    }

    /* function to insert a new_node in a list. */
    void sortedInsert(Node new_node)
    {
        Node current;

        /* Special case for head node */
        if (head == null || head.data >= new_node.data) {
            new_node.next = head;
            head = new_node;
        }
        else {

            /* Locate the node before
            point of insertion. */
            current = head;

            while (current.next != null && current.next.data < new_node.data)
                current = current.next;

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    /*Utility functions*/

    /* Function to create a node */
    Node newNode(int data)
    {
        Node x = new Node(data);
        return x;
    }

    /* Function to print linked list */
    void printList()
    {
        Node temp = head;
        while (temp != null) {
            Console.Write(temp.data + " ");
            temp = temp.next;
        }
    }

    /* Driver code */
    public static void Main(String[] args)
    {
        LinkedList llist = new LinkedList();
        Node new_node;

        new_node = llist.newNode(5);
        llist.sortedInsert(new_node);

        new_node = llist.newNode(10);
        llist.sortedInsert(new_node);

        new_node = llist.newNode(7);
        llist.sortedInsert(new_node);

        new_node = llist.newNode(3);
        llist.sortedInsert(new_node);

        new_node = llist.newNode(1);
        llist.sortedInsert(new_node);

        new_node = llist.newNode(9);
        llist.sortedInsert(new_node);

        Console.WriteLine("Created Linked List");
        llist.printList();
    }
}

/* This code is contributed by 29AjayKumar */

Javascript

<script>
// javascript Program to insert in a sorted list
var head; // head of list

    /* Linked list Node */
     class Node {
            constructor(val) {
                this.data = val;
                this.next = null;
            }
        }

    /*
     * function to insert a new_node in a list.
     */
    function sortedInsert( new_node) {
        var current;

        /* Special case for head node */
        if (head == null || head.data >= new_node.data) {
            new_node.next = head;
            head = new_node;
        } else {

            /* Locate the node before point of insertion. */
            current = head;

            while (current.next != null && current.next.data < new_node.data)
                current = current.next;

            new_node.next = current.next;
            current.next = new_node;
        }
    }

    /* Utility functions */

    /* Function to create a node */
    function newNode(data) {
         x = new Node(data);
        return x;
    }

    /* Function to print linked list */
    function printList() {
         temp = head;
        while (temp != null) {
            document.write(temp.data + " ");
            temp = temp.next;
        }
    }

    /* Driver function to test above methods */
        var new_node;
        new_node = newNode(5);
        sortedInsert(new_node);
        new_node = newNode(10);
        sortedInsert(new_node);
        new_node = newNode(7);
        sortedInsert(new_node);
        new_node = newNode(3);
        sortedInsert(new_node);
        new_node = newNode(1);
        sortedInsert(new_node);
        new_node = newNode(9);
        sortedInsert(new_node);
        document.write("Created Linked List<br/>");
        printList();

// This code is contributed by aashish1995
</script>

Output

Created Linked List
1 3 5 7 9 10 

Complexity Analysis:

• Time Complexity: O(n). 
  Only one traversal of the list is needed.
• Auxiliary Space: O(1). 
  No extra space is needed.

Shorter Implementation using double pointers:
Thanks to Murat M Ozturk for providing this solution. Please see Murat M Ozturk’s comment below for complete function. The code uses double-pointer to keep track of the next pointer of the previous node (after which new node is being inserted).
Note that below line in code changes current to have address of next pointer in a node. 

   current = &((*current)->next);

Also, note below comments. 

    /* Copies the value-at-address current to
      new_node's next pointer*/ 
    new_node->next = *current; 

    /* Fix next pointer of the node (using its address) 
       after which new_node is being inserted */ 
    *current = new_node;  

Time Complexity: O(n) 
Auxiliary Space: O(1) because it is using constant space

Approach:

• If the linked list is empty, then make the new node as the head and return.
• Traverse the linked list till either current node becomes None or current node’s value is greater than the new node’s value.
• If the new node is to be inserted at the beginning, then the head of the linked list needs to be changed to the new node.
• If the new node is to be inserted at any other position, then the previous node’s next should point to the new node, and the new node’s next should point to the current node.
• Return the head of the linked list.

Code for another approach:

C++

#include <iostream>
using namespace std;

class Node {
public:
    int data;
    Node* next;

    Node(int data) {
        this->data = data;
        next = nullptr;
    }
};

class LinkedList {
private:
    Node* head;

public:
    LinkedList() {
        head = nullptr;
    }

    void sortedInsert(Node* new_node) {
        if (head == nullptr) {
            head = new_node;
            return;
        }

        Node* prev = nullptr;
        Node* current = head;
        while (current && current->data < new_node->data) {
            prev = current;
            current = current->next;
        }

        if (prev == nullptr) {
            new_node->next = head;
            head = new_node;
        }
        else {
            new_node->next = current;
            prev->next = new_node;
        }
    }

    void push(int data) {
        Node* new_node = new Node(data);
        new_node->next = head;
        head = new_node;
    }

    void printList() {
        Node* temp = head;
        while (temp != nullptr) {
            cout << temp->data << " ";
            temp = temp->next;
        }
    }
};

int main() {
    LinkedList llist;
    Node* new_node = new Node(5);
    llist.sortedInsert(new_node);
    new_node = new Node(10);
    llist.sortedInsert(new_node);
    new_node = new Node(7);
    llist.sortedInsert(new_node);
    new_node = new Node(3);
    llist.sortedInsert(new_node);
    new_node = new Node(1);
    llist.sortedInsert(new_node);
    new_node = new Node(9);
    llist.sortedInsert(new_node);
    cout << "Create Linked List" << endl;
    llist.printList();
    return 0;
}

Java

class Node {
    int data;
    Node next;

    Node(int data) {
        this.data = data;
        next = null;
    }
}

public class LinkedList {
    Node head; // head of the list

    static class Node {
        int data;
        Node next;

        Node(int d) {
            data = d;
            next = null;
        }
    }

    // Function to insert a new node in a sorted way
    public void sortedInsert(Node new_node) {
        if (head == null) {
            head = new_node;
            return;
        }

        Node current = head;
        Node prev = null;
        while (current != null && current.data < new_node.data) {
            prev = current;
            current = current.next;
        }

        if (prev == null) {
            new_node.next = head;
            head = new_node;
        } else {
            new_node.next = current;
            prev.next = new_node;
        }
    }

    // Function to print the linked list
    public void printList() {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }
    }

    // Driver code
    public static void main(String[] args) {
        LinkedList list = new LinkedList();

        Node new_node = new Node(5);
        list.sortedInsert(new_node);

        new_node = new Node(10);
        list.sortedInsert(new_node);

        new_node = new Node(7);
        list.sortedInsert(new_node);

        new_node = new Node(3);
        list.sortedInsert(new_node);

        new_node = new Node(1);
        list.sortedInsert(new_node);

        new_node = new Node(9);
        list.sortedInsert(new_node);

        System.out.println("Created Linked List");
        list.printList();
    }
}

Python3

# Node class
class Node:

  # Constructor to initialize the node object
  def __init__(self, data):
    self.data = data
    self.next = None

class LinkedList:

  # Function to initialize head
  def __init__(self):
    self.head = None

  # Function to insert a new node in a sorted way
  def sortedInsert(self, new_node):
    if self.head is None:
      self.head = new_node
      return

    prev = None
    current = self.head
    while current and current.data < new_node.data:
      prev = current
      current = current.next

    if prev is None:
      new_node.next = self.head
      self.head = new_node
    else:
      new_node.next = current
      prev.next = new_node

  # Utility function to print the LinkedList
  def printList(self):
    temp = self.head
    while temp:
      print(temp.data, end=" ")
      temp = temp.next

# Driver program
llist = LinkedList()
new_node = Node(5)
llist.sortedInsert(new_node)
new_node = Node(10)
llist.sortedInsert(new_node)
new_node = Node(7)
llist.sortedInsert(new_node)
new_node = Node(3)
llist.sortedInsert(new_node)
new_node = Node(1)
llist.sortedInsert(new_node)
new_node = Node(9)
llist.sortedInsert(new_node)
print("Create Linked List")
llist.printList()

C#

using System;

public class Node
{
    public int data;
    public Node next;

    public Node(int data)
    {
        this.data = data;
        this.next = null;
    }
}

public class LinkedList
{
    public Node head;

    public LinkedList()
    {
        this.head = null;
    }

    public void SortedInsert(Node newNode)
    {
        if (this.head == null)
        {
            this.head = newNode;
            return;
        }

        Node prev = null;
        Node current = this.head;
        while (current != null && current.data < newNode.data)
        {
            prev = current;
            current = current.next;
        }

        if (prev == null)
        {
            newNode.next = this.head;
            this.head = newNode;
        }
        else
        {
            newNode.next = current;
            prev.next = newNode;
        }
    }

    public void PrintList()
    {
        Node temp = this.head;
        while (temp != null)
        {
            Console.Write(temp.data + " ");
            temp = temp.next;
        }
        Console.WriteLine();
    }
}

public class Program
{
    public static void Main()
    {
        LinkedList llist = new LinkedList();
        Node newNode = new Node(5);
        llist.SortedInsert(newNode);
        newNode = new Node(10);
        llist.SortedInsert(newNode);
        newNode = new Node(7);
        llist.SortedInsert(newNode);
        newNode = new Node(3);
        llist.SortedInsert(newNode);
        newNode = new Node(1);
        llist.SortedInsert(newNode);
        newNode = new Node(9);
        llist.SortedInsert(newNode);
        Console.WriteLine("Create Linked List");
        llist.PrintList();
    }
}

Javascript

class Node {
    constructor(data) {
        this.data = data;
        this.next = null;
    }
}

class LinkedList {
    constructor() {
        this.head = null;
    }

    sortedInsert(newNode) {
        if (this.head == null) {
            this.head = newNode;
            return;
        }

        let prev = null;
        let current = this.head;
        while (current != null && current.data < newNode.data) {
            prev = current;
            current = current.next;
        }

        if (prev == null) {
            newNode.next = this.head;
            this.head = newNode;
        } else {
            newNode.next = current;
            prev.next = newNode;
        }
    }

    printList() {
        let temp = this.head;
        while (temp != null) {
            console.log(temp.data + " ");
            temp = temp.next;
        }
        console.log();
    }
}

let llist = new LinkedList();
let newNode = new Node(5);
llist.sortedInsert(newNode);
newNode = new Node(10);
llist.sortedInsert(newNode);
newNode = new Node(7);
llist.sortedInsert(newNode);
newNode = new Node(3);
llist.sortedInsert(newNode);
newNode = new Node(1);
llist.sortedInsert(newNode);
newNode = new Node(9);
llist.sortedInsert(newNode);
console.log("Create Linked List");
llist.printList();

Output

Create Linked List
1 3 5 7 9 10 

The time complexity of this algorithm is O(n) where n is the number of nodes in the linked list. 
The space complexity is O(1) as it uses constant extra space.