sum-root-to-leaf-numbers——dfs

Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path1->2->3which represents the number123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / 
  2   3

The root-to-leaf path1->2represents the number12.
The root-to-leaf path1->3represents the number13.

Return the sum = 12 + 13 =25.

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int sumNumbers(TreeNode *root) {
        if(root==NULL)
            return 0;
        res=0;
        dfs(root,0);
        return res;
    }
    void dfs(TreeNode *root,int num){
        if(root!=NULL){
            num=num*10+root->val;
        }
        if(root->left==NULL&&root->right==NULL){
            res+=num;
        }
        if(root->left!=NULL){
            dfs(root->left,num);
        }
        if(root->right!=NULL){
            dfs(root->right,num);
        }
    }
    int res;
};