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);}};