222. Number of nodes in a complete binary tree

 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 {
12     vector<int> ans;
13 public:
14     int countNodes(TreeNode* root) 
15     {
16         if(!root) return 0;
17         queue<TreeNode*> q;
18         q.push(root);
19         while(!q.empty())
20         {
21             int n = q.size();
22             for(int i = 0;i < n;i ++)
23             {
24                 TreeNode* temp = q.front();
25                 q.pop();
26                 ans.push_back(temp->val);
27 
28                 if(temp->left) q.push(temp->left);
29                 if(temp->right) q.push(temp->right);
30             }
31         }
32         return ans.size();
33     }
34 };