running_sum_1d_array

from typing import List

def running_sum(nums: List[int]) -> List[int]:
    """
    Compute the running sum of a 1D array.

    Given an integer array nums, return the running sum such that:
        running_sum[i] = nums[0] + nums[1] + ... + nums[i]

    Time Complexity: O(n)
    Space Complexity: O(n)

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

    Returns:
        List[int]: Running sum of the input list.

    Example:
        >>> running_sum([1, 2, 3, 4])
        [1, 3, 6, 10]
    """
    n = len(nums)
    if n == 0:
        return []

    ans = [0] * n
    ans[0] = nums[0]

    for i in range(1, n):
        ans[i] = ans[i - 1] + nums[i]

    return ans


if __name__ == "__main__":
    # quick test cases
    examples = [
        ([1, 2, 3, 4], [1, 3, 6, 10]),
        ([1, 1, 1, 1, 1], [1, 2, 3, 4, 5]),
        ([3, 1, 2, 10, 1], [3, 4, 6, 16, 17]),
        ([], []),
    ]

    for arr, expected in examples:
        print(f"{arr} -> {running_sum(arr)} (expected {expected})")