the highest sum of any k consecutive elements in the array

highest_sum_sliding_window.py

def highestSum(arr, k):
    highest_sum = float('-inf')
    n = len(arr)

    # n must not be smaller than k
    if n < k:
        return -1

    # Compute sum of first window of size k
    window_sum = sum([arr[i] for i in range(k)])

    # Compute sums of remaining windows by 
    # removing first element of previous 
    # window and adding last element of 
    # current window. 
    for i in range(n - k):
        window_sum = window_sum - arr[i] + arr[i + k]
        highest_sum = max(highest_sum, window_sum)

    return highest_sum

This code will not work in certain edge cases. Try the following input:

arr = [2, 3, 7, 1, 1, 1]
k = 3

The result should be 12 but your code returns 11.

It's easy to correct though:

1. Remove line #2
2. Add the following code to line #11:

highest_sum  = window_sum