Sum Root to Leaf Numbers问题及解法

问题描述：

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.

示例：

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

.

问题分析：

典型的根先序遍历问题，到结点root时，和s = s * 10 + root->val,若root是叶子节点，则总和sum = sum + s；

过程详见代码：

/**
* 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 {
public:
int sumNumbers(TreeNode* root) {
int sum = 0;
sumofpath(root, sum, 0);
return sum;
}

void sumofpath(TreeNode* root,int& sum,int s)
{
if (root == NULL) return;
s = s * 10 + root->val;
if (root->left == NULL && root->right == NULL)
sum += s;
sumofpath(root->left, sum, s);
sumofpath(root->right, sum, s);

}
};