Nested list weight sum

Time: O(N); Space: O(H); easy

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:

Input: nestedList = [[1,1],2,[1,1]]

Output: 10

Explanation:

  • Four 1’s at depth 2, one 2 at depth 1, 4 * 1 * 2 + 1 * 2 * 1 = 10

Example 2:

Input: nestedList = [1,[4,[6]]]

Output: 27

Explanation:

  • One 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 4 * 2 + 6 * 3 = 27

1. Recursion

[1]:

class Solution1(object):
    """
    Time: O(N)
    Space: O(H)
    """
    def depthSum(self, nestedList):
        """
        :type nestedList: List[NestedInteger]
        :rtype: int
        """
        def depthSumHelper(nestedList, depth):
            res = 0
            for l in nestedList:
                if l.isInteger():
                    res += l.getInteger() * depth
                else:
                    res += depthSumHelper(l.getList(), depth + 1)
            return res

        return depthSumHelper(nestedList, 1)

[2]:

s = Solution1()

nestedList = [[1,1],2,[1,1]]
assert s.depthSum(nestedList) == 10

nestedList = [1,[4,[6]]]
assert s.depthSum(nestedList) == 27

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-872528c2eabb> in <module>
      2
      3 nestedList = [[1,1],2,[1,1]]
----> 4 assert s.depthSum(nestedList) == 10
      5
      6 nestedList = [1,[4,[6]]]

<ipython-input-1-bdb64c39c809> in depthSum(self, nestedList)
     17                     res += depthSumHelper(l.getList(), depth + 1)
     18             return res
---> 19         return depthSumHelper(nestedList, 1)
     20

<ipython-input-1-bdb64c39c809> in depthSumHelper(nestedList, depth)
     12             res = 0
     13             for l in nestedList:
---> 14                 if l.isInteger():
     15                     res += l.getInteger() * depth
     16                 else:

AttributeError: 'list' object has no attribute 'isInteger'