# Maximum sum of K consecutive nodes in the given Linked List

Given a linked list, the task is tofind the maximum sum obtained by adding any k consecutive nodes of linked list.

**Examples:**

Input:1 -> 2 -> 3 -> 4 -> 5 -> 6 -> NULL, K = 5

Output:20

Maximum sum is obtained by adding last 5 nodes

Input:2 -> 5 -> 3 -> 6 -> 4 -> 1 -> 7 -> NULL, K = 4

Output:18

**Approach:** The idea is to use a sliding window of size k, keep track of sum of current window and update maximum sum if required. To implement sliding window two pointers can be used to represent starting and ending point. At each step first the value of node pointed by start is subtracted from current sum and the value of node pointed by end is added to current sum. This sum is compared to maximum sum and result is updated if required. The start and end pointers are incremented by one at each step.

Below is the implementation of above approach:

`// C++ implementation of the approach ` `#include <bits/stdc++.h> ` `using` `namespace` `std; ` ` ` `// Structure of a node ` `struct` `Node { ` ` ` `int` `data; ` ` ` `Node* next; ` `}; ` ` ` `// Function to create new node ` `Node* newNode(` `int` `data) ` `{ ` ` ` `Node* node = ` `new` `Node; ` ` ` `node->next = NULL; ` ` ` `node->data = data; ` ` ` `return` `node; ` `} ` ` ` `// Function to return the maximum sum of ` `// k consecutive nodes ` `int` `findMaxSum(Node* head, ` `int` `k) ` `{ ` ` ` `// To store current window sum ` ` ` `int` `sum = 0; ` ` ` ` ` `// To store maximum sum ` ` ` `int` `maxSum = 0; ` ` ` ` ` `// Pointer to the start of window ` ` ` `Node* start = head; ` ` ` ` ` `// Pointer to the end of window ` ` ` `Node* end = head; ` ` ` ` ` `int` `i; ` ` ` ` ` `// Find the sum of first k nodes ` ` ` `for` `(i = 0; i < k; i++) { ` ` ` `sum += end->data; ` ` ` `end = end->next; ` ` ` `} ` ` ` ` ` `maxSum = sum; ` ` ` ` ` `// Move window by one step and ` ` ` `// update sum. Node pointed by ` ` ` `// start is excluded from current ` ` ` `// window so subtract it. Node ` ` ` `// pointed by end is added to ` ` ` `// current window so add its value. ` ` ` `while` `(end != NULL) { ` ` ` ` ` `// Subtract the starting element ` ` ` `// from previous window ` ` ` `sum -= start->data; ` ` ` `start = start->next; ` ` ` ` ` `// Add the element next to the end ` ` ` `// of previous window ` ` ` `sum += end->data; ` ` ` `end = end->next; ` ` ` ` ` `// Update the maximum sum so far ` ` ` `maxSum = max(maxSum, sum); ` ` ` `} ` ` ` ` ` `return` `maxSum; ` `} ` ` ` `// Driver code ` `int` `main() ` `{ ` ` ` `Node* head = newNode(1); ` ` ` `head->next = newNode(2); ` ` ` `head->next->next = newNode(3); ` ` ` `head->next->next->next = newNode(4); ` ` ` `head->next->next->next->next = newNode(5); ` ` ` `head->next->next->next->next->next = newNode(6); ` ` ` ` ` `int` `k = 5; ` ` ` ` ` `cout << findMaxSum(head, k); ` ` ` ` ` `return` `0; ` `} ` |

*chevron_right*

*filter_none*

**Output:**

20

**Time Complexity:** O(n)

**Auxiliary Space:** O(1)

## Recommended Posts:

- Check if absolute difference of consecutive nodes is 1 in Linked List
- Construct a Maximum Sum Linked List out of two Sorted Linked Lists having some Common nodes
- Maximum sum contiguous nodes in the given linked list
- Splitting starting N nodes into new Circular Linked List while preserving the old nodes
- Append odd position nodes in reverse at the end of even positioned nodes in a Linked List
- Delete N nodes after M nodes of a linked list
- Linked List Sum of Nodes Between 0s
- Find the sum of last n nodes of the given Linked List
- Find sum of even and odd nodes in a linked list
- Sum of the nodes of a Singly Linked List
- Sum of all distinct nodes in a linked list
- Sum of all odd frequency nodes of the Linked List
- Sum and Product of all the nodes which are less than K in the linked list
- Sum of the alternate nodes of linked list
- Linked List Product of Nodes Between 0s

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.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.