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

.

思路：这道题使用递归。这道题思路比较明确，目标是把从根到叶子节点的所有路径得到的整数累加起来，递归条件即是把当前的sum*10加上当前结点的值传入函数，进行递归，最终把左右子树的总和相加。结束条件就是如果一个结点是叶子结点，那么我们应该累加到结果总和中。

/**
* 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 sumPath(TreeNode *root,int sum)
{
if(root==NULL)
return 0;
sum=sum*10+root->val;
if(root->left==NULL&&root->right==NULL)
{
return sum;
}
if(root->left==NULL)
return sumPath(root->right,sum);
if(root->right==NULL)
return sumPath(root->left,sum);
return sumPath(root->left,sum)+sumPath(root->right,sum);
}
int sumNumbers(TreeNode *root) {
int sum=0;
return sumPath(root,sum);
}
};