129. 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.

【思路】递归，深度优先搜索，每一层的节点值等于上一层值乘以10再加上当前值。

/**
 * 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:
    void DFS(TreeNode* p, int currSum, int& Sum)
    {
       if(p == NULL)
            return;
        if(!p->left && !p->right)
        {
            Sum += (10* currSum)+ p->val;
            
        }else
        {
            DFS(p->left, 10* currSum+ p->val, Sum);
            DFS(p->right, 10* currSum+ p->val, Sum);
        }
     
    }
    
    int sumNumbers(TreeNode* root) {
        int result = 0;
        DFS(root, 0, result);
        return result;
    }
};