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.

/**
 * 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) {
        vector<int> leaf;
        int sum = 0;
        if(root){
            leafnum(root, leaf, 0);
            int len = leaf.size();
            for(int i=0;i<len; i++)
                sum += leaf[i];
            return sum;
        }
        return NULL;
    }
    void leafnum(TreeNode *root, vector<int> &leaf, int crt){
        if(root->left == NULL && root->right == NULL){
            leaf.push_back(root->val + crt * 10);
            return;
        }
        if(root->left){
            leafnum(root->left, leaf, root->val + crt * 10);
        }
        if(root->right){
            leafnum(root->right, leaf, root->val + crt * 10);
        }
    }
};