637. Average of Levels in Binary Tree

https://leetcode.com/problems/average-of-levels-in-binary-tree/

Python

class Solution:
    def averageOfLevels(self, root: Optional[TreeNode]) -> List[float]:
        def travel(node, level: int, result: list):
            if not node:
                return

            if level == len(result):
                result.append([1, node.val])
            else:
                result[level][0] += 1
                result[level][1] += node.val

            travel(node.left, level+1, result)
            travel(node.right, level+1, result)

        result = [[1, float(root.val)]]
        travel(root, 0, result)
        return [n[1]/n[0] for n in result]