Sum Root to Leaf Numbers

问题：根节点到叶子结点的所有权值和
分析：从根节点遍历，若遍历到叶子结点，则sum+其路径的所有权值和

/**

 * 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 sum;

    void dfs(TreeNode *root,int num)

    {

        if(root->left==NULL && root->right==NULL) sum+=num;

        if(root->left) dfs(root->left,num*10+root->left->val);

        if(root->right) dfs(root->right,num*10+root->right->val);

    }

    int sumNumbers(TreeNode *root) {

        if(root==NULL) return 0;

        sum=0;

        int num=0;

        dfs(root,root->val);

        return sum;

    }

};