Count Complete Tree Nodes 统计完全二叉树的节点数

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.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:

/*
超时
    int countNodes(TreeNode* root) {
        return solve(root);
    }
    
    int solve(TreeNode *root)
    {
        if(root == NULL)
            return 0;
        int left=solve(root->left);
        int right=solve(root->right);
        return left+right+1;
    }
    */
    
    int countNodes(TreeNode* root) {
        if(root==NULL)
            return 0;
        int numL=0,numR=0;
        TreeNode *lt=root;
        TreeNode *rt=root;
        while(lt!=NULL)
        {
            numL++;
            lt=lt->left;
        }
        while(rt!=NULL)
        {
            numR++;
            rt=rt->right;
        }
        
        if(numL==numR)
            return pow(2,numL)-1;
        else
            return countNodes(root->left)+countNodes(root->right)+1;
    }
};