Maximum sum of a contiguous subarray

January 1, 2024

Problem #

Given a list of integers, find the maximum sum of a contiguous subarray with length 3.

Solution #

Here’s the Python code to find the maximum sum of a contiguous subarray of length 3 in a given list of integers:

def maxSumSubarrayOfSizeThree(nums):
    """
    Find the maximum sum of a contiguous subarray of size 3.

    Args:
    nums (List[int]): A list of integers.

    Returns:
    int: The maximum sum of a contiguous subarray of size 3.
    """
    if len(nums) < 3:
        return "List is too short for a subarray of size 3."

    max_sum = current_sum = sum(nums[:3])

    for i in range(3, len(nums)):
        current_sum = current_sum - nums[i - 3] + nums[i]
        max_sum = max(max_sum, current_sum)

    return max_sum

# Example usage
nums_list = [1, 2, 3, 4, 5]
max_sum = maxSumSubarrayOfSizeThree(nums_list)
print(max_sum)

For the example list [1, 2, 3, 4, 5], the function calculates the maximum sum of a contiguous subarray of size 3, which is 12 (from the subarray [3, 4, 5]).

The function works by first checking if the list is long enough to have a subarray of size 3. It then initializes the maximum sum (max_sum) with the sum of the first three elements. It iterates through the list, updating the current sum (current_sum) for each subarray of size 3 by subtracting the element that is no longer in the subarray and adding the new element. After each iteration, it updates max_sum if a higher sum is found.