completeTreeNodes.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution
{
public:
    int countNodes(TreeNode *root)
    {
        if (!root)
            return 0;

        int leftHeight = computeHeight(root->left);
        int rightHeight = computeHeight(root->right);

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

private:
    int computeHeight(TreeNode *node)
    {
        int height = 0;

        while (node)
        {
            height++;
            node = node->left;
        }

        return height;
    }
};