Sum Root to Leaf Numbers

Sum Root to Leaf Numbers

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.

递归，每个节点的值都是当前节点*10+右节点 + 当前节点*10+左节点。

/**
 * 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 dfs(root, 0);
        
    }
private:


    int dfs(TreeNode *root, int sum){
        if(!root) return 0;
        if(!root->left && !root->right) {
            return sum*10 + root->val;
        }
        
        return dfs(root->left, sum*10 + root->val) + 
                dfs(root->right, sum*10 + root->val);
    }
};