Sum Root to Leaf Numbers

 1 class Solution {
 2 public:
 3     int sumNumbers(TreeNode *root) {
 4         vector<int> path;
 5         int sum = 0;
 6         dfs(root,path,sum);
 7         return sum;
 8     }
 9     void dfs(TreeNode * root, vector<int> & path, int & sum){
10         if(!root) return;
11         path.push_back(root->val);
12         if(!root->left && !root->right){
13             int len = path.size();
14             for(int i = 0; i < len; i++)
15                 sum += path[i]*pow(10.0,len-i-1);
16         }
17         if(root->left) dfs(root->left,path,sum);
18         if(root->right) dfs(root->right,path,sum);
19         path.pop_back();
20     }
21 };