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Count Complete Tree Nodes

EasyTrees & Graphs

Given the root of a complete binary tree (as a level-order array), return the number of nodes.

A complete binary tree has every level fully filled except possibly the last, which is filled from left to right.

Example:

Input:
1,2,3,4,5,6
Output:
6
Reasoning:
  • The input array 1,2,3,4,5,6 represents a level-order traversal of the complete binary tree.
  • We can visualize the tree as:
    • Level 1: 1
    • Level 2: 2, 3
    • Level 3: 4, 5, 6
  • Since it's a complete binary tree, every level is fully filled except possibly the last, which is filled from left to right.
  • The number of nodes is equal to the number of elements in the input array, so the output is 66.

Constraints:

  • 0 <= number of nodes <= 5 * 10^4
  • 0 <= Node.val <= 5 * 10^4
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