222. Count Complete Tree Nodes

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

计算完全二叉树的节点数目。满二叉树的节点数是2^h-1， h为树的高度。

/** * 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:       int countNodes(TreeNode* root) {       /*------递归算法超时       if(root==NULL) return 0;       int count = 1;       count += countNodes(root->left);       count += countNodes(root->right);       return count;       -------------------*/       if(root==NULL) return 0;       int leftH = getLeftHeight(root);       int rightH = getRightHeight(root);       if(leftH==rightH)        return (1<<leftH)-1;       else       {         return countNodes(root->left) + countNodes(root->right)+1;          }    }    int getLeftHeight(TreeNode* root)    {        if(root==NULL) return 0;        int h = 1;        while(root->left)        {            h++;            root= root->left;        }        return h;    }    int getRightHeight(TreeNode* root)    {        if(root==NULL) return 0;        int h = 1;        while(root->right)        {            h++;            root= root->right;        }        return h;    }};