【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

.
解题思路：用DFS算法搜索每条路经上的数，求出每条路经数字组合在一起的数，再将这些数相加。

代码：

/**
* 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) {
int Sum=0,CurrSum=0;
build_path(Sum, CurrSum, root);
return Sum;
}
private:
void build_path(int &Sum, int &CurrSum, TreeNode *root){
if(root==nullptr)return;
CurrSum=CurrSum*10+root->val;
if(!root->left&&!root->right){
Sum+=CurrSum;
}else{
build_path(Sum, CurrSum, root->left);
build_path(Sum, CurrSum, root->right);
}
CurrSum=(CurrSum-root->val)/10;
}
};