222. Count Complete Tree Nodes

https://leetcode.com/problems/count-complete-tree-nodes

Python

class Solution:
    def countNodes(self, root: Optional[TreeNode]) -> int:
        result = self._travel(root, 0)
        return result

    def _travel(self, node, counter) -> int:
        if not node:
            return 0

        return 1 + self._travel(node.left, 0) + self._travel(node.right, 0)