129. 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.

解答：这道题其实就是dfs，然后传入一个临时的和直到叶结点，然后把临时的和加入到最终的result中。主要是很多边界条件处理得不好。花了一些时间。

/**
* 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 {
private:
int result=0;
public:
void sum(TreeNode* root,int res)
{
if((root->left==NULL)&&(root->right==NULL))
{
res=res*10+root->val;
result+=res;
return ;
}
res=res*10+root->val;
if(root->left)sum(root->left,res);
if(root->right)sum(root->right,res);

}int sumNumbers(TreeNode* root) {    if(root==NULL) return 0;    if(root->left==NULL&&root->right==NULL) return root->val;    sum(root,0);    return result;}

};