[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 };