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);    }};