[Leetcode 39] 129 Sum Root to Leaf Numbers

Problem:

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.

Analysis:

Simple tree DFS problem. 

Code:

/**
 * 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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (root == NULL) return 0;
        
        int pathSum = 0, total = 0;
        helper(root, pathSum, total);
        
        return total;
    }
    
    int helper(TreeNode *node, int pathSum, int& total) {
        if (node->left==NULL && node->right==NULL) {
            total += pathSum*10 + node->val;
        }
        
        pathSum = pathSum*10 + node->val;
        if(node->left != NULL)
            helper(node->left, pathSum, total);
            
        if (node->right != NULL)
            helper(node->right, pathSum, total);
    }
    
};

Attention: