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# Find kth node from Middle towards Head of a Linked List

• Difficulty Level : Basic
• Last Updated : 08 Jun, 2021

Given a Linked List and a number K. The task is to print the value of the K-th node from the middle towards the beginning of the List. If no such element exists, then print “-1”.
Note: Position of middle node is: (n/2)+1, where n is the total number of nodes in the list.
Examples

```Input :  List is 1->2->3->4->5->6->7
K= 2
Output : 2

Input :  list is 7->8->9->10->11->12
K = 3
Output : 7```

Traverse the List from beginning to end and count the total number of nodes. Now, suppose is the total number of nodes in the List. Therefore, the middle node will be at the position (n/2)+1. Now, the task remains to print the node at (n/2 + 1 – k)th position from the head of the List.
Below is the implementation of the above idea:

## C++

 `// CPP program to find kth node from middle``// towards Head of the Linked List` `#include ` `using` `namespace` `std;` `// Linked list node``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `/* Given a reference (pointer to ``   ``pointer) to the head of a list``   ``and an int, push a new node on``   ``the front of the list. */``void` `push(``struct` `Node** head_ref,``          ``int` `new_data)``{``    ``struct` `Node* new_node = ``new` `Node;``    ``new_node->data = new_data;``    ``new_node->next = (*head_ref);``    ``(*head_ref) = new_node;``}` `// Function to count number of nodes``int` `getCount(``struct` `Node* head)``{``    ``int` `count = 0; ``// Initialize count``    ``struct` `Node* current = head; ``// Initialize current``    ``while` `(current != NULL) {``        ``count++;``        ``current = current->next;``    ``}``    ``return` `count;``}` `// Function to get the kth node from the mid``// towards begin of the linked list``int` `printKthfrommid(``struct` `Node* head_ref, ``int` `k)``{``    ``// Get the count of total number of``    ``// nodes in the linked list``    ``int` `n = getCount(head_ref);` `    ``int` `reqNode = ((n / 2 + 1) - k);` `    ``// If no such node exists, return -1``    ``if` `(reqNode <= 0) {``        ``return` `-1;``    ``}` `    ``// Find node at position reqNode``    ``else` `{``        ``struct` `Node* current = head_ref;` `        ``// the index of the``        ``// node we're currently``        ``// looking at``        ``int` `count = 1;``        ``while` `(current != NULL) {``            ``if` `(count == reqNode)``                ``return` `(current->data);``            ``count++;``            ``current = current->next;``        ``}``    ``}``}` `// Driver code``int` `main()``{``    ``// start with empty list``    ``struct` `Node* head = NULL;``    ``int` `k = 2;` `    ``// create linked list``    ``// 1->2->3->4->5->6->7``    ``push(&head, 7);``    ``push(&head, 6);``    ``push(&head, 5);``    ``push(&head, 4);``    ``push(&head, 3);``    ``push(&head, 2);``    ``push(&head, 1);` `    ``cout << printKthfrommid(head, 2);` `    ``return` `0;``}`

## Java

 `// Java program to find Kth node from mid``// of a linked list in single traversal` `// Linked list node``class` `Node``{``    ``int` `data;``    ``Node next;``    ``Node(``int` `d)``    ``{``        ``this``.data = d;``        ``this``.next = ``null``;``    ``}``}` `class` `LinkedList``{``    ``Node start;``    ``LinkedList()``    ``{``        ``start = ``null``;``    ``}``    ` `    ``// Function to push node at head``    ``public` `void` `push(``int` `data)``    ``{``        ``if``(``this``.start == ``null``)``        ``{``            ``Node temp = ``new` `Node(data);``            ``this``.start = temp;``        ``}``        ``else``        ``{``            ``Node temp = ``new` `Node(data);``            ``temp.next = ``this``.start;``            ``this``.start = temp;``        ``}``    ``}``    ` `    ``//method to get the count of node``    ``public` `int` `getCount(Node start)``    ``{``        ``Node temp = start;``        ``int` `cnt = ``0``;``        ``while``(temp != ``null``)``        ``{``            ``temp = temp.next;``            ``cnt++;``        ``}``        ``return` `cnt;``    ``}``    ` `    ``// Function to get the kth node from the mid``    ``// towards begin of the linked list``    ``public` `int` `printKthfromid(Node start, ``int` `k)``    ``{``        ``// Get the count of total number of``        ``// nodes in the linked list``        ``int` `n = getCount(start);``        ``int` `reqNode = ((n + ``1``) / ``2``) - k;` `        ``// If no such node exists, return -1``        ``if``(reqNode <= ``0``)``            ``return` `-``1``;``        ``else``        ``{``            ``Node current = start;``            ``int` `count = ``1``,ans = ``0``;``            ``while` `(current != ``null``)``            ``{``                ``if` `(count == reqNode)``                ``{``                    ``ans = current.data;``                    ``break``;``                ``}``                ``count++;``                ``current = current.next;``            ``}``            ``return` `ans;``        ``}``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``    ``// create linked list``        ``// 1->2->3->4->5->6->7``    ``LinkedList ll = ``new` `LinkedList();``        ``ll.push(``7``);``        ``ll.push(``6``);``        ``ll.push(``5``);``        ``ll.push(``4``);``        ``ll.push(``3``);``        ``ll.push(``2``);``        ``ll.push(``1``);``        ``System.out.println(ll.printKthfromid(ll.start, ``2``));``    ``}``}` `// This Code is contributed by Adarsh_Verma`

## Python3

 `# Python3 program to find kth node from``# middle towards Head of the Linked List` `# Node class``class` `Node:` `    ``# Function to initialise the node object``    ``def` `__init__(``self``, data):``        ``self``.data ``=` `data``        ``self``.``next` `=` `None` `# Function to insert a node at the``# beginning of the linked list``def` `push(head, data):``    ``if` `not` `head:` `        ``# Return new node``        ``return` `Node(data)``    ` `    ``# allocate node``    ``new_node ``=` `Node(data)``    ` `    ``# link the old list to the new node``    ``new_node.``next` `=` `head``    ` `    ``# move the head to point``    ``# to the new node``    ``head ``=` `new_node``    ``return` `head` `# Function to count number of nodes``def` `getCount(head):``    ` `    ``count ``=` `0` `# Initialize count``    ``current ``=` `head ``# Initialize current``    ``while` `(current ):``        ``count ``=` `count ``+` `1``        ``current ``=` `current.``next``    ` `    ``return` `count` `# Function to get the kth node from the mid``# towards begin of the linked list``def` `printKthfrommid(head_ref, k):` `    ``# Get the count of total number of``    ``# nodes in the linked list``    ``n ``=` `getCount(head_ref)` `    ``reqNode ``=` `int``((n ``/` `2` `+` `1``) ``-` `k)` `    ``# If no such node exists, return -1``    ``if` `(reqNode <``=` `0``) :``        ``return` `-``1``    ` `    ``# Find node at position reqNode``    ``else` `:``        ``current ``=` `head_ref` `        ``# the index of the``        ``# node we're currently``        ``# looking at``        ``count ``=` `1``        ``while` `(current) :``            ``if` `(count ``=``=` `reqNode):``                ``return` `(current.data)``            ``count ``=` `count ``+` `1``            ``current ``=` `current.``next``        ` `# Driver Code``if` `__name__``=``=``'__main__'``:``    ` `    ``# start with empty list``    ``head ``=` `None``    ``k ``=` `2` `    ``# create linked list``    ``# 1.2.3.4.5.6.7``    ``head ``=` `push(head, ``7``)``    ``head ``=` `push(head, ``6``)``    ``head ``=` `push(head, ``5``)``    ``head ``=` `push(head, ``4``)``    ``head ``=` `push(head, ``3``)``    ``head ``=` `push(head, ``2``)``    ``head ``=` `push(head, ``1``)`` ` `    ``print``(printKthfrommid(head, ``2``))``    ` `# This code is contributed by Arnab Kundu`

## C#

 `// C# program to find Kth node from mid``// of a linked list in single traversal``using` `System;` `// Linked list node``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node next;``    ``public` `Node(``int` `d)``    ``{``        ``this``.data = d;``        ``this``.next = ``null``;``    ``}``}` `public` `class` `LinkedList``{``    ``Node start;``    ``LinkedList()``    ``{``        ``start = ``null``;``    ``}``    ` `    ``// Function to push node at head``    ``public` `void` `push(``int` `data)``    ``{``        ``if``(``this``.start == ``null``)``        ``{``            ``Node temp = ``new` `Node(data);``            ``this``.start = temp;``        ``}``        ``else``        ``{``            ``Node temp = ``new` `Node(data);``            ``temp.next = ``this``.start;``            ``this``.start = temp;``        ``}``    ``}``    ` `    ``//method to get the count of node``    ``public` `int` `getCount(Node start)``    ``{``        ``Node temp = start;``        ``int` `cnt = 0;``        ``while``(temp != ``null``)``        ``{``            ``temp = temp.next;``            ``cnt++;``        ``}``        ``return` `cnt;``    ``}``    ` `    ``// Function to get the kth node from the mid``    ``// towards begin of the linked list``    ``public` `int` `printKthfromid(Node start, ``int` `k)``    ``{``        ``// Get the count of total number of``        ``// nodes in the linked list``        ``int` `n = getCount(start);``        ``int` `reqNode = ((n + 1) / 2) - k;` `        ``// If no such node exists, return -1``        ``if``(reqNode <= 0)``            ``return` `-1;``        ``else``        ``{``            ``Node current = start;``            ``int` `count = 1,ans = 0;``            ``while` `(current != ``null``)``            ``{``                ``if` `(count == reqNode)``                ``{``                    ``ans = current.data;``                    ``break``;``                ``}``                ``count++;``                ``current = current.next;``            ``}``            ``return` `ans;``        ``}``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``// create linked list``        ``// 1->2->3->4->5->6->7``        ``LinkedList ll = ``new` `LinkedList();``        ``ll.push(7);``        ``ll.push(6);``        ``ll.push(5);``        ``ll.push(4);``        ``ll.push(3);``        ``ll.push(2);``        ``ll.push(1);``        ``Console.WriteLine(ll.printKthfromid(ll.start, 2));``    ``}``}` `// This code is contributed by Rajput-Ji`

## Javascript

 ``
Output
`2`

Time Complexity: O(n), where n is the length of the list.
Auxiliary Space: O(1)

Method 2 :

This method focuses on finding the K-th node from the middle towards the beginning of the List using two pointers.

Prerequisite: two pointers method in  https://www.geeksforgeeks.org/write-a-c-function-to-print-the-middle-of-the-linked-list/

Traverse linked list using two pointers named as slow and fast. Move the fast pointer B times if it reaches the end, then no answer exists print “-1” else start moving fast and slow pointers simultaneously when the fast pointer reaches the end, the answer will the value of the slow pointer.

Below is the implementation of the above idea:

## C++

 `// Using two pointers``// CPP program to find kth node from middle``// towards Head of the Linked List`  `#include ` `using` `namespace` `std;` `// Linked list node``struct` `Node {``    ``int` `data;``    ``struct` `Node* next;``};` `/* Given a reference (pointer to ``   ``pointer) to the head of a list``   ``and an int, push a new node on``   ``the front of the list. */``void` `push(``struct` `Node** head_ref,``          ``int` `new_data)``{``    ``struct` `Node* new_node = ``new` `Node;``    ``new_node->data = new_data;``    ``new_node->next = (*head_ref);``    ``(*head_ref) = new_node;``}` `// Function to get the kth node from the mid``// towards begin of the linked list``int` `printKthfrommid(``struct` `Node* head_ref, ``int` `k)``{``    ``struct` `Node* slow = head_ref;``    ``struct` `Node* fast = head_ref;  ``// initializing fast and slow pointers``    ` `    ``for``( ``int` `i = 0 ; i < k ; i++ )``     ``{``       ``if``(fast && fast->next)``       ``{``         ``fast = fast->next->next;  ``// moving the fast pointer``       ``}``       ``else``       ``{``         ``return` `-1;   ``// If no such node exists, return -1``       ``}``     ``}``     ` `     ``while``(fast && fast->next)``     ``{``       ``slow  = slow->next;``       ``fast  = fast->next->next;``     ``}``     ` `    ``return` `slow->data;``}`  `// Driver code``int` `main()``{``    ``// start with empty list``    ``struct` `Node* head = NULL;``    ``int` `k = 2;` `    ``// create linked list``    ``// 1->2->3->4->5->6->7``    ``push(&head, 7);``    ``push(&head, 6);``    ``push(&head, 5);``    ``push(&head, 4);``    ``push(&head, 3);``    ``push(&head, 2);``    ``push(&head, 1);` `    ``cout << printKthfrommid(head, 2);` `    ``return` `0;``}`
Output
`2`

Time Complexity: O(n), where n is the length of the list.
Auxiliary Space: O(1)

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