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.

 

这道求根到叶节点数字之和的题跟之前的求很类似，都是利用DFS递归来解，这道题由于不是单纯的把各个节点的数字相加，而是每到一个新的数字，要把原来的数字扩大10倍之后再相加。代码如下：

 

/** * Definition for binary tree * 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 sumNumbersDFS(root, 0);    }    int sumNumbersDFS(TreeNode *root, int sum) {        if (!root) return 0;        sum = sum * 10 + root->val;        if (!root->left && !root->right) return sum;        return sumNumbersDFS(root->left, sum) + sumNumbersDFS(root->right, sum);    }};