37. Sum Root to Leaf Numbers FROM Leetcode

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.

解题之法

/**
 * 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 sumNumbers(TreeNode *root) {
       return  sumNumberUtil(root,0);
        
    }
    // preorder
    int sumNumberUtil(TreeNode* node, int val)
    {
        if(node==NULL)
        return 0;
        
        val= val*10+node->val;
        if(node->left==NULL && node->right==NULL)
        {
            return val;
        }
        
        return sumNumberUtil(node->left,val)+sumNumberUtil(node->right, val);
    }
};