【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 2h nodes inclusive at the last level h.

Solution 1

class Solution {
public:
    int countNodes(TreeNode* root) {
        int lh = 0, rh = 0;
        TreeNode* lch = root, *rch = root;
        
        while (lch) {
            ++lh;
            lch = lch->left;
        }
        while (rch) {
            ++rh;
            rch = rch->right;
        }
        if (lh == rh)
            return pow(2, lh) - 1;
        return countNodes(root->left) + countNodes(root->right) + 1;
    }
};