Sum Root to Leaf Numbers深度优先计算路径和

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