leetcode Sum Root to Leaf Numbers

题目连接

https://leetcode.com/problems/sum-root-to-leaf-numbers/  

Sum Root to Leaf Numbers

Description

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.

/**
 * 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 ans;
	int sumNumbers(TreeNode* root) {
		if (!root) return 0;
		ans = 0;
		dfs(root, 0);
		return ans;
	}
	void dfs(TreeNode *x, int v) {
		if (!x) return;
		if (!x->left && !x->right) {
			ans += x->val + v * 10;
		}
		dfs(x->left, v * 10 + x->val);
		dfs(x->right, v * 10 + x->val);
	}
};