Maximum Sum Subarray of Size K

Problem

Given a list of integers arr and an integer k, return the largest sum among all contiguous subarrays of length exactly k.

Use a fixed-size sliding window: add the entering element and remove the leaving one to update the sum in O(1). Return None if k <= 0 or the list is shorter than k; values may be negative.

Hint

Slide the window one step at a time and compare each new window sum with the best so far.

Test cases

case 1

in: [[2,1,5,1,3,2],3]

expected: 9

case 2

in: [[1],1]

expected: 1

case 3

in: [[1,2],3]

expected: null

case 4

in: [[-3,-1,-2],2]

expected: -3

case 5

in: [[-5,4,-1,2],2]

expected: 3

Starter codePython

def max_sum_subarray_k(arr, k):
    # Your code here
    pass

5 test cases · run your code against them in the editor