LeetCode 222. Count Complete Tree Nodes

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

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 2^h nodes inclusive at the last level h.

    int countHelper(TreeNode* root) {  // do it recursively! 
        if(!root) return 0;
        TreeNode* l = root;
        TreeNode* r = root;
        int leftCount = 0, rightCount = 0;
        while(l) {
            leftCount++;
            l = l->left;
        }
        
        while(r) {
            rightCount++;
            r = r->right;
        }
        if(leftCount == rightCount) return pow(2, rightCount) - 1;
        else return countHelper(root->left) + countHelper(root->right) + 1;
    }
    int countNodes(TreeNode* root) {
        return countHelper(root);
    }