Sum Root to Leaf Numbers

/**

 * Definition for a binary tree node.

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int sumNumbers(TreeNode* root) {

        return sum(root,0);

    }

    int sum(TreeNode *root,int num){

        if(root==NULL) return 0;

        if(root->left ==NULL && root->right == NULL) return num*10+root->val; 

        return sum(root->left,num*10+root->val)+sum(root->right,num*10+root->val);

    }

};

  

递归的思想