计算一棵完全二叉树上节点的数目

class Solution {
public:
    int countNodes(TreeNode* root) {
        if(!root) return 0;
        TreeNode * leftNode = root;
        TreeNode * rightNode = root;
        int left = 0;
        int right = 0;
        while(leftNode->left){
            left++;
            leftNode=leftNode->left;
        }
        while(rightNode->right){
            right++;
            rightNode = rightNode->right;
        }
        if(left == right) return (1 << (left + 1)) - 1;
        else return 1 + countNodes(root->left) + countNodes(root->right);
    }
};