[Leetcode] Sum Root to Leaf Numbers

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

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

For example,

    1
   / 
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

递归求解，注意中间变量与全局变量的保存。

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     void getSum(TreeNode *root, int &sum, int val) {
13         if (root->right == NULL && root->left == NULL) {
14             sum += val;
15             return;
16         } 
17         if (root->left != NULL) {
18             getSum(root->left, sum, val * 10 + root->left->val);
19         }
20         if (root->right != NULL) {
21             getSum(root->right, sum, val * 10 + root->right->val);
22         }
23     }
24     
25     int sumNumbers(TreeNode *root) {
26         if (root == NULL) {
27             return 0;
28         }
29         int sum = 0;
30         getSum(root, sum, root->val);
31         return sum;
32     }
33 };