LeetCode Sum Root to Leaf Numbers

题目：

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

.

/**
* 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 sumNumbers(TreeNode *root) {
if(root == NULL)
return 0;
return dfs(root, 0);

}
//自顶向下
int dfs(TreeNode *root, int pre) {
int sum = pre * 10 + root->val;
if(root->left == NULL && root->right == NULL)
return sum;
if(root->right == NULL)
return dfs(root->left, sum);
if(root->left == NULL)
return dfs(root->right, sum);
return dfs(root->left, sum) + dfs(root->right, sum);
}
};