# Leetcode 222 - Count complete tree nodes

`Note`

`Note`

Given the root of a complete binary tree, return the number of the nodes in the tree.

According to Wikipedia, every level, except possibly the last, is completely filled in a complete binary tree, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.

Design an algorithm that runs in less than O(n) time complexity.

**Example**

1 | Input: root = [1,2,3,4,5,6] |

`Iteration`

1 | /** |

`Recursion`

1 | /** |