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 2hnodes inclusive at the last level h.
1 /** 2 * Definition for a binary tree node. 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */ 10 class Solution { 11 public: 12 int countNodes(TreeNode* root) { 13 if(root==NULL) 14 return 0; 15 TreeNode* tmp=root->left; 16 int leftheight=1; 17 int rightheight=1; 18 while(tmp!=NULL) 19 { 20 tmp=tmp->left; 21 leftheight++; 22 } 23 tmp=root->right; 24 while(tmp!=NULL) 25 { 26 tmp=tmp->right; 27 rightheight++; 28 } 29 if(leftheight==rightheight) 30 { 31 return (1<<leftheight)-1; 32 } 33 else 34 return countNodes(root->left)+countNodes(root->right)+1; 35 } 36 };