题目：
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.
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) { return Solution::sumFromRoot2Leaf(root, 0); } static int sumFromRoot2Leaf(TreeNode* root, int upperVal) { if ( !root ) return 0; if ( !root->left && !root->right ) return upperVal*10+root->val; return Solution::sumFromRoot2Leaf(root->left, upperVal*10+root->val) + Solution::sumFromRoot2Leaf(root->right, upperVal*10+root->val); } };
tips：
一开始想自低向上算，后来发现自顶向下算，每次传入上一层的值比较科学。
原文：http://www.cnblogs.com/xbf9xbf/p/4511477.html