Nested list summation

depth_sum.py

def depthSum(nestedList):
    """
    :type nestedList: List[Things] where Things can be an int or more List[Things]
    :rtype: int
    """
    # This is a depth-first search as we need to find the deepest level and return sum
    # at each depth
    return dfs(nestedList, 1)
        
                
def dfs(items, depth):
    weighted_sum = 0
    for item in items:
        if not isinstance(item, list):
            weighted_sum += depth * item
        else:
            weighted_sum += dfs(item, depth+1)
    return weighted_sum

problem.md

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1: Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1)

Example 2: Given the list [1,[4,[6]]], return 27. (one 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4*2 + 6*3 = 27)