# Insert node into the middle of the linked list

Given a linked list containing n nodes. The problem is to insert a new node with data x at the middle of the list. If n is even, then insert the new node after the (n/2)th node, else insert the new node after the (n+1)/2th node.

Examples:

```Input : list: 1->2->4->5
x = 3
Output : 1->2->3->4->5

Input : list: 5->10->4->32->16
x = 41
Output : 5->10->4->41->32->16
```

## Recommended: Please solve it on PRACTICE first, before moving on to the solution.

Method 1(Using length of the linked list):
Find the number of nodes or length of the linked using one traversal. Let it be len. Calculate c = (len/2), if len is even, else c = (len+1)/2, if len is odd. Traverse again the first c nodes and insert the new node after the cth node.

## C++

 `// C++ implementation to insert node at the middle ` `// of the linked list ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// structure of a node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// function to create and return a node ` `Node* getNode(``int` `data) ` `{ ` `    ``// allocating space ` `    ``Node* newNode = (Node*)``malloc``(``sizeof``(Node)); ` ` `  `    ``// inserting the required data ` `    ``newNode->data = data; ` `    ``newNode->next = NULL; ` `    ``return` `newNode; ` `} ` ` `  `// function to insert node at the middle ` `// of the linked list ` `void` `insertAtMid(Node** head_ref, ``int` `x) ` `{ ` `    ``// if list is empty ` `    ``if` `(*head_ref == NULL) ` `        ``*head_ref = getNode(x); ` `    ``else` `{ ` ` `  `        ``// get a new node ` `        ``Node* newNode = getNode(x); ` ` `  `        ``Node* ptr = *head_ref; ` `        ``int` `len = 0; ` ` `  `        ``// calculate length of the linked list ` `        ``//, i.e, the number of nodes ` `        ``while` `(ptr != NULL) { ` `            ``len++; ` `            ``ptr = ptr->next; ` `        ``} ` ` `  `        ``// 'count' the number of nodes after which ` `        ``//  the new node is to be inserted ` `        ``int` `count = ((len % 2) == 0) ? (len / 2) : ` `                                    ``(len + 1) / 2; ` `        ``ptr = *head_ref; ` ` `  `        ``// 'ptr' points to the node after which  ` `        ``// the new node is to be inserted ` `        ``while` `(count-- > 1) ` `            ``ptr = ptr->next; ` ` `  `        ``// insert the 'newNode' and adjust the ` `        ``// required links ` `        ``newNode->next = ptr->next; ` `        ``ptr->next = newNode; ` `    ``} ` `} ` ` `  `// function to display the linked list ` `void` `display(Node* head) ` `{ ` `    ``while` `(head != NULL) { ` `        ``cout << head->data << ``" "``; ` `        ``head = head->next; ` `    ``} ` `} ` ` `  `// Driver program to test above ` `int` `main() ` `{ ` `    ``// Creating the list 1->2->4->5 ` `    ``Node* head = NULL; ` `    ``head = getNode(1); ` `    ``head->next = getNode(2); ` `    ``head->next->next = getNode(4); ` `    ``head->next->next->next = getNode(5); ` ` `  `    ``cout << ``"Linked list before insertion: "``; ` `    ``display(head); ` ` `  `    ``int` `x = 3; ` `    ``insertAtMid(&head, x); ` ` `  `    ``cout << ``"\nLinked list after insertion: "``; ` `    ``display(head); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation to insert node ` `// at the middle of the linked list ` `import` `java.util.*; ` `import` `java.lang.*; ` `import` `java.io.*; ` ` `  `class` `LinkedList ` `{ ` `    ``static` `Node head; ``// head of list ` ` `  `    ``/* Node Class */` `    ``static` `class` `Node { ` `        ``int` `data; ` `        ``Node next; ` `         `  `        ``// Constructor to create a new node ` `        ``Node(``int` `d) { ` `            ``data = d; ` `            ``next = ``null``; ` `        ``} ` `    ``} ` ` `  `    ``// function to insert node at the  ` `    ``// middle of the linked list ` `    ``static` `void` `insertAtMid(``int` `x) ` `    ``{ ` `        ``// if list is empty ` `        ``if` `(head == ``null``) ` `            ``head = ``new` `Node(x); ` `        ``else` `{ ` `            ``// get a new node ` `            ``Node newNode = ``new` `Node(x); ` ` `  `            ``Node ptr = head; ` `            ``int` `len = ``0``; ` ` `  `            ``// calculate length of the linked list ` `            ``//, i.e, the number of nodes ` `            ``while` `(ptr != ``null``) { ` `                ``len++; ` `                ``ptr = ptr.next; ` `            ``} ` ` `  `            ``// 'count' the number of nodes after which ` `            ``// the new node is to be inserted ` `            ``int` `count = ((len % ``2``) == ``0``) ? (len / ``2``) : ` `                                        ``(len + ``1``) / ``2``; ` `            ``ptr = head; ` ` `  `            ``// 'ptr' points to the node after which  ` `            ``// the new node is to be inserted ` `            ``while` `(count-- > ``1``) ` `                ``ptr = ptr.next; ` ` `  `            ``// insert the 'newNode' and adjust  ` `            ``// the required links ` `            ``newNode.next = ptr.next; ` `            ``ptr.next = newNode; ` `        ``} ` `    ``} ` ` `  `    ``// function to display the linked list ` `    ``static` `void` `display() ` `    ``{ ` `        ``Node temp = head; ` `        ``while` `(temp != ``null``)  ` `        ``{ ` `            ``System.out.print(temp.data + ``" "``); ` `            ``temp = temp.next; ` `        ``} ` `    ``} ` ` `  `    ``// Driver program to test above ` `    ``public` `static` `void` `main (String[] args)  ` `    ``{  ` `        ``// Creating the list 1.2.4.5 ` `        ``head = ``null``; ` `        ``head = ``new` `Node(``1``); ` `        ``head.next = ``new` `Node(``2``); ` `        ``head.next.next = ``new` `Node(``4``); ` `        ``head.next.next.next = ``new` `Node(``5``); ` `         `  `        ``System.out.println(``"Linked list before "``+ ` `                           ``"insertion: "``); ` `        ``display(); ` ` `  `        ``int` `x = ``3``; ` `        ``insertAtMid(x); ` ` `  `        ``System.out.println(``"\nLinked list after"``+ ` `                           ``" insertion: "``); ` `        ``display(); ` `    ``}  ` `} ` ` `  `// This article is contributed by Chhavi `

## Python3

 `# Python3 implementation to insert node ` `# at the middle of a linked list ` ` `  `# Node class ` `class` `Node: ` ` `  `    ``# constructor to create a new node ` `    ``def` `__init__(``self``, data): ` `        ``self``.data ``=` `data ` `        ``self``.``next` `=` `None` ` `  `# function to insert node at the ` `# middle of linked list given the head ` `def` `insertAtMid(head, x): ` ` `  `    ``if``(head ``=``=` `None``): ``#if the list is empty ` `        ``head ``=` `Node(x) ` `    ``else``: ` `         `  `        ``# create a new node for the value ` `        ``# to be inserted ` `        ``newNode ``=` `Node(x) ` ` `  `        ``ptr ``=` `head ` `        ``length ``=` `0` `         `  `        ``# calcualte the length of the linked ` `        ``# list ` `        ``while``(ptr !``=` `None``): ` `            ``ptr ``=` `ptr.``next` `            ``length ``+``=` `1` ` `  `        ``# 'count' the number of node after which ` `        ``# the new node has to be inserted ` `        ``if``(length ``%` `2` `=``=` `0``): ` `            ``count ``=` `length ``/` `2`  `        ``else``: ` `            ``(length ``+` `1``) ``/` `2` ` `  `        ``ptr ``=` `head ` ` `  `        ``# move ptr to the node after which ` `        ``# the new node has to inserted ` `        ``while``(count > ``1``): ` `            ``count ``-``=` `1` `            ``ptr ``=` `ptr.``next` ` `  `        ``# insert the 'newNode' and adjust ` `        ``# links accordingly ` `        ``newNode.``next` `=` `ptr.``next` `        ``ptr.``next` `=` `newNode ` ` `  `# function to displat the linked list ` `def` `display(head): ` `    ``temp ``=` `head ` `    ``while``(temp !``=` `None``): ` `        ``print``(``str``(temp.data), end ``=` `" "``) ` `        ``temp ``=` `temp.``next` ` `  `# Driver Code ` ` `  `# Creating the linked list 1.2.4.5 ` `head ``=` `Node(``1``) ` `head.``next` `=` `Node(``2``) ` `head.``next``.``next` `=` `Node(``4``) ` `head.``next``.``next``.``next` `=` `Node(``5``) ` ` `  `print``(``"Linked list before insertion: "``, end ``=` `"") ` `display(head) ` ` `  `# inserting 3 in the middle of the linked list. ` `x ``=` `3` `insertAtMid(head, x) ` ` `  `print``(``"\nLinked list after insertion: "` `, end ``=` `"") ` `display(head) ` ` `  `# This code is contributed by Pranav Devarakonda `

## C#

 `// C# implementation to insert node  ` `// at the middle of the linked list  ` `using` `System; ` ` `  `public` `class` `LinkedList  ` `{  ` `    ``static` `Node head; ``// head of list  ` ` `  `    ``/* Node Class */` `    ``public` `class` `Node  ` `    ``{  ` `        ``public` `int` `data;  ` `        ``public` `Node next;  ` `         `  `        ``// Constructor to create a new node  ` `        ``public` `Node(``int` `d)  ` `        ``{  ` `            ``data = d;  ` `            ``next = ``null``;  ` `        ``}  ` `    ``}  ` ` `  `    ``// function to insert node at the  ` `    ``// middle of the linked list  ` `    ``static` `void` `insertAtMid(``int` `x)  ` `    ``{  ` `        ``// if list is empty  ` `        ``if` `(head == ``null``)  ` `            ``head = ``new` `Node(x);  ` `        ``else`  `        ``{  ` `            ``// get a new node  ` `            ``Node newNode = ``new` `Node(x);  ` ` `  `            ``Node ptr = head;  ` `            ``int` `len = 0;  ` ` `  `            ``// calculate length of the linked list  ` `            ``//, i.e, the number of nodes  ` `            ``while` `(ptr != ``null``) ` `            ``{  ` `                ``len++;  ` `                ``ptr = ptr.next;  ` `            ``}  ` ` `  `            ``// 'count' the number of nodes after which  ` `            ``// the new node is to be inserted  ` `            ``int` `count = ((len % 2) == 0) ? (len / 2) :  ` `                                        ``(len + 1) / 2;  ` `            ``ptr = head;  ` ` `  `            ``// 'ptr' points to the node after which  ` `            ``// the new node is to be inserted  ` `            ``while` `(count-- > 1)  ` `                ``ptr = ptr.next;  ` ` `  `            ``// insert the 'newNode' and adjust  ` `            ``// the required links  ` `            ``newNode.next = ptr.next;  ` `            ``ptr.next = newNode;  ` `        ``}  ` `    ``}  ` ` `  `    ``// function to display the linked list  ` `    ``static` `void` `display()  ` `    ``{  ` `        ``Node temp = head;  ` `        ``while` `(temp != ``null``)  ` `        ``{  ` `            ``Console.Write(temp.data + ``" "``);  ` `            ``temp = temp.next;  ` `        ``}  ` `    ``}  ` ` `  `    ``// Driver code  ` `    ``public` `static` `void` `Main ()  ` `    ``{  ` `        ``// Creating the list 1.2.4.5  ` `        ``head = ``null``;  ` `        ``head = ``new` `Node(1);  ` `        ``head.next = ``new` `Node(2);  ` `        ``head.next.next = ``new` `Node(4);  ` `        ``head.next.next.next = ``new` `Node(5);  ` `         `  `        ``Console.WriteLine(``"Linked list before "``+  ` `                        ``"insertion: "``);  ` `        ``display();  ` ` `  `        ``int` `x = 3;  ` `        ``insertAtMid(x);  ` ` `  `        ``Console.WriteLine(``"\nLinked list after"``+  ` `                        ``" insertion: "``);  ` `        ``display();  ` `    ``}  ` `}  ` ` `  `/* This code contributed by PrinciRaj1992 */`

Output:

```Linked list before insertion: 1 2 4 5
Linked list after insertion: 1 2 3 4 5
```

Time Complexity: O(n)

Method 2(Using two pointers):
Based on the tortoise and hare algorithm which uses two pointers, one known as slow and the other known as fast. This algorithm helps in finding the middle node of the linked list. It is explained in the front and black split procedure of this post. Now, you can insert the new node after the middle node obtained from the above process. This approach requires only a single traversal of the list.

## C++

 `// C++ implementation to insert node at the middle ` `// of the linked list ` `#include ` ` `  `using` `namespace` `std; ` ` `  `// structure of a node ` `struct` `Node { ` `    ``int` `data; ` `    ``Node* next; ` `}; ` ` `  `// function to create and return a node ` `Node* getNode(``int` `data) ` `{ ` `    ``// allocating space ` `    ``Node* newNode = (Node*)``malloc``(``sizeof``(Node)); ` ` `  `    ``// inserting the required data ` `    ``newNode->data = data; ` `    ``newNode->next = NULL; ` `} ` ` `  `// function to insert node at the middle ` `// of the linked list ` `void` `insertAtMid(Node** head_ref, ``int` `x) ` `{ ` `    ``// if list is empty ` `    ``if` `(*head_ref == NULL) ` `        ``*head_ref = getNode(x); ` ` `  `    ``else` `{ ` `        ``// get a new node ` `        ``Node* newNode = getNode(x); ` ` `  `        ``// assign values to the slow and fast  ` `        ``// pointers ` `        ``Node* slow = *head_ref; ` `        ``Node* fast = (*head_ref)->next; ` ` `  `        ``while` `(fast && fast->next) { ` ` `  `            ``// move slow pointer to next node ` `            ``slow = slow->next; ` ` `  `            ``// move fast pointer two nodes at a time ` `            ``fast = fast->next->next; ` `        ``} ` ` `  `        ``// insert the 'newNode' and adjust the ` `        ``// required links ` `        ``newNode->next = slow->next; ` `        ``slow->next = newNode; ` `    ``} ` `} ` ` `  `// function to display the linked list ` `void` `display(Node* head) ` `{ ` `    ``while` `(head != NULL) { ` `        ``cout << head->data << ``" "``; ` `        ``head = head->next; ` `    ``} ` `} ` ` `  `// Driver program to test above ` `int` `main() ` `{ ` `    ``// Creating the list 1->2->4->5 ` `    ``Node* head = NULL; ` `    ``head = getNode(1); ` `    ``head->next = getNode(2); ` `    ``head->next->next = getNode(4); ` `    ``head->next->next->next = getNode(5); ` ` `  `    ``cout << ``"Linked list before insertion: "``; ` `    ``display(head); ` ` `  `    ``int` `x = 3; ` `    ``insertAtMid(&head, x); ` ` `  `    ``cout << ``"\nLinked list after insertion: "``; ` `    ``display(head); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation to insert node  ` `// at the middle of the linked list ` `import` `java.util.*; ` `import` `java.lang.*; ` `import` `java.io.*; ` ` `  `class` `LinkedList ` `{ ` `    ``static` `Node head; ``// head of list ` ` `  `    ``/* Node Class */` `    ``static` `class` `Node { ` `        ``int` `data; ` `        ``Node next; ` `         `  `        ``// Constructor to create a new node ` `        ``Node(``int` `d) { ` `            ``data = d; ` `            ``next = ``null``; ` `        ``} ` `    ``} ` ` `  `    ``// function to insert node at the  ` `    ``// middle of the linked list ` `    ``static` `void` `insertAtMid(``int` `x) ` `    ``{ ` `        ``// if list is empty ` `        ``if` `(head == ``null``) ` `        ``head = ``new` `Node(x); ` ` `  `        ``else` `{ ` `            ``// get a new node ` `            ``Node newNode = ``new` `Node(x); ` ` `  `            ``// assign values to the slow  ` `            ``// and fast pointers ` `            ``Node slow = head; ` `            ``Node fast = head.next; ` ` `  `            ``while` `(fast != ``null` `&& fast.next  ` `                                  ``!= ``null``)  ` `            ``{ ` `                ``// move slow pointer to next node ` `                ``slow = slow.next; ` ` `  `                ``// move fast pointer two nodes  ` `                ``// at a time ` `                ``fast = fast.next.next; ` `            ``} ` ` `  `            ``// insert the 'newNode' and adjust  ` `            ``// the required links ` `            ``newNode.next = slow.next; ` `            ``slow.next = newNode; ` `        ``} ` `    ``} ` ` `  `    ``// function to display the linked list ` `    ``static` `void` `display() ` `    ``{ ` `        ``Node temp = head; ` `        ``while` `(temp != ``null``)  ` `        ``{ ` `            ``System.out.print(temp.data + ``" "``); ` `            ``temp = temp.next; ` `        ``} ` `    ``} ` ` `  `    ``// Driver program to test above ` `    ``public` `static` `void` `main (String[] args)  ` `    ``{  ` `        ``// Creating the list 1.2.4.5 ` `        ``head = ``null``; ` `        ``head = ``new` `Node(``1``); ` `        ``head.next = ``new` `Node(``2``); ` `        ``head.next.next = ``new` `Node(``4``); ` `        ``head.next.next.next = ``new` `Node(``5``); ` `         `  `        ``System.out.println(``"Linked list before"``+ ` `                           ``" insertion: "``); ` `        ``display(); ` ` `  `        ``int` `x = ``3``; ` `        ``insertAtMid(x); ` ` `  `        ``System.out.println(``"\nLinked list after"``+ ` `                           ``" insertion: "``); ` `        ``display(); ` `    ``}  ` `} ` ` `  `// This article is contributed by Chhavi `

## Python3

 `# Python implementation to insert node  ` `# at the middle of the linked list  ` ` `  `# Node Class ` `class` `Node : ` `    ``def` `__init__(``self``, d): ` `        ``self``.data ``=` `d  ` `        ``self``.``next` `=` `None` `         `  `class` `LinkedList:  ` ` `  `    ``# function to insert node at the  ` `    ``# middle of the linked list ` `    ``def` `__init__(``self``): ` `        ``self``.head ``=` `None` `     `  `    ``# 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  ` `         `  `    ``def` `insertAtMid(``self``, x): ` `         `  `        ``# if list is empty  ` `        ``if` `(``self``.head ``=``=` `None``):  ` `            ``self``.head ``=` `Node(x)  ` ` `  `        ``else``:  ` `             `  `            ``# get a new node  ` `            ``newNode ``=` `Node(x)  ` ` `  `            ``# assign values to the slow  ` `            ``# and fast pointers  ` `            ``slow ``=` `self``.head ` `            ``fast ``=` `self``.head.``next` ` `  `            ``while` `(fast !``=` `None` `and`  `                   ``fast.``next` `!``=` `None``):  ` `                 `  `                ``# move slow pointer to next node  ` `                ``slow ``=` `slow.``next` ` `  `                ``# move fast pointer two nodes  ` `                ``# at a time  ` `                ``fast ``=` `fast.``next``.``next` ` `  `            ``# insert the 'newNode' and  ` `            ``# adjust the required links  ` `            ``newNode.``next` `=` `slow.``next` `            ``slow.``next` `=` `newNode ` ` `  `    ``# function to display the linked list  ` `    ``def` `display(``self``): ` `        ``temp ``=` `self``.head  ` `        ``while` `(temp !``=` `None``):  ` `            ``print``(temp.data, end ``=` `" "``), ` `            ``temp ``=` `temp.``next` ` `  `# Driver Code ` ` `  `# Creating the list 1.2.4.5  ` `ll ``=` `LinkedList() ` `ll.push(``5``) ` `ll.push(``4``) ` `ll.push(``2``) ` `ll.push(``1``) ` `print``(``"Linked list before insertion: "``), ` `ll.display() ` ` `  `x ``=` `3` `ll.insertAtMid(x) ` ` `  `print``(``"\nLinked list after insertion: "``), ` `ll.display() ` ` `  `# This code is contributed by prerna saini `

## C#

 `// C# implementation to insert node  ` `// at the middle of the linked list ` `using` `System; ` ` `  `public` `class` `LinkedList ` `{ ` `    ``static` `Node head; ``// head of list ` ` `  `    ``/* Node Class */` `    ``class` `Node  ` `    ``{ ` `        ``public` `int` `data; ` `        ``public` `Node next; ` `         `  `        ``// Constructor to create a new node ` `        ``public` `Node(``int` `d)  ` `        ``{ ` `            ``data = d; ` `            ``next = ``null``; ` `        ``} ` `    ``} ` ` `  `    ``// function to insert node at the  ` `    ``// middle of the linked list ` `    ``static` `void` `insertAtMid(``int` `x) ` `    ``{ ` `        ``// if list is empty ` `        ``if` `(head == ``null``) ` `        ``head = ``new` `Node(x); ` ` `  `        ``else` `        ``{ ` `            ``// get a new node ` `            ``Node newNode = ``new` `Node(x); ` ` `  `            ``// assign values to the slow  ` `            ``// and fast pointers ` `            ``Node slow = head; ` `            ``Node fast = head.next; ` ` `  `            ``while` `(fast != ``null` `&& fast.next  ` `                                ``!= ``null``)  ` `            ``{ ` `                ``// move slow pointer to next node ` `                ``slow = slow.next; ` ` `  `                ``// move fast pointer two nodes  ` `                ``// at a time ` `                ``fast = fast.next.next; ` `            ``} ` ` `  `            ``// insert the 'newNode' and adjust  ` `            ``// the required links ` `            ``newNode.next = slow.next; ` `            ``slow.next = newNode; ` `        ``} ` `    ``} ` ` `  `    ``// function to display the linked list ` `    ``static` `void` `display() ` `    ``{ ` `        ``Node temp = head; ` `        ``while` `(temp != ``null``)  ` `        ``{ ` `            ``Console.Write(temp.data + ``" "``); ` `            ``temp = temp.next; ` `        ``} ` `    ``} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `Main (String[] args)  ` `    ``{  ` `        ``// Creating the list 1.2.4.5 ` `        ``head = ``null``; ` `        ``head = ``new` `Node(1); ` `        ``head.next = ``new` `Node(2); ` `        ``head.next.next = ``new` `Node(4); ` `        ``head.next.next.next = ``new` `Node(5); ` `         `  `        ``Console.WriteLine(``"Linked list before"``+ ` `                        ``" insertion: "``); ` `        ``display(); ` ` `  `        ``int` `x = 3; ` `        ``insertAtMid(x); ` ` `  `        ``Console.WriteLine(``"\nLinked list after"``+ ` `                        ``" insertion: "``); ` `        ``display(); ` `    ``}  ` `} ` ` `  `// This code is contributed by Rajput-Ji `

Output:

```Linked list before insertion: 1 2 4 5
Linked list after insertion: 1 2 3 4 5
```

Time Complexity: O(n)

This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.