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

.
题意是一条路径，由根结点到叶子结点，代表一个数，根是高位，一直这样下去。例如例子里，有12和13这两个数，然后求所有路径数之和。其实题目挺简单的，就是一个深搜，所以用递归的话是最简洁易懂的，代码如下。

Code(LeetCode运行3ms)

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