LeetCode OJ - Sum Root to Leaf Numbers

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.

解题思路：

利用深搜找到所有路径上表示的数，然后把它们加起来。

代码：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void dfs(TreeNode *root, int cur_ans, int &ans) {
        if (root == NULL) return;
        
        if (root->left == NULL && root->right == NULL) ans += (cur_ans * 10 + root->val);
        if (root->left != NULL) dfs(root->left, cur_ans * 10 + root->val, ans);
        if (root->right != NULL) dfs(root->right, cur_ans * 10 + root->val, ans);
        return;
    }
    int sumNumbers(TreeNode *root) {
        int ans = 0;
        dfs(root, 0, ans);
        
        return ans;
    }
};