Best k-Day Sponsorship

Ravi runs a juice stall and has the sales of each of the last n days. A sponsor will fund exactly k consecutive days and pays according to the total sales of those days, so Ravi wants the k-day block with the highest total. Return that maximum total.

Examples

Example 1

Input:  sales = [2, 1, 5, 1, 3, 2], k = 3
Output: 9

With k = 3 the possible blocks are (2, 1, 5) = 8, (1, 5, 1) = 7, (5, 1, 3) = 9 and (1, 3, 2) = 6. The best block is the third one, so the sponsor pays for a total of 9.

Example 2

Input:  sales = [4, 4, 4], k = 2
Output: 8

Constraints

sales holds one day’s sales per entry, and k is between 1 and the number of days. The k days must be next to each other.

Return the largest total any k consecutive days reach.

How to solve it

Hint

“Exactly k consecutive days, maximum total” = maximum sum of a subarray of fixed length k.

Approach: Fixed-size sliding window

Compute the sum of the first k days.
Slide the window one day right: add the new day, subtract the day that left.
Keep the maximum total seen.

Check with the example. Windows of 3 days: 2+1+5=8, 1+5+1=7, 5+1+3=9, 1+3+2=6 → best is 9.

Complexity: O(n) time, O(1) space.

The reference solutions in all four languages are in the Solutions tab of the workspace below.