222. Count Complete Tree Nodes

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Problem

Given a complete binary tree, count the number of nodes.

Note:

Definition of a complete binary tree from Wikipedia: In a complete binary tree every level, except possibly the last, is completely filled, 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.

Example:

Input:
    1
   / \
  2   3
 / \  /
4  5 6

Output: 6

Code

class Solution {
    public int countNodes(TreeNode root) {
        int left = leftDepth(root);
        int right = rightDepth(root);

        if(left == right){
            return (1 << left) - 1;
        } else {
            return 1 + countNodes(root.left) + countNodes(root.right);
        }
    }

    private int leftDepth(TreeNode root){
        int res = 0;
        while(root != null){
            root = root.left;
            res++;
        }

        return res;
    }

    private int rightDepth(TreeNode root){
        int res = 0;
        while(root != null){
            root = root.right;
            res++;
        }

        return res;
    }
}