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

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/**  * 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;     } };