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.

solution:

class Solution {
public:
int i = 0;
int sumNumbers(TreeNode* root) {
if (root == NULL) return 0;
return sum(root, 0);
}
int sum(TreeNode * root, int val)
{
if (root->left == NULL && root->right == NULL) return (val * 10 + root->val);
if (root->left != NULL && root->right == NULL) return sum(root->left, val * 10 + root->val);
if (root->left == NULL && root->right != NULL) return sum(root->right, val * 10 + root->val);
if (root->left != NULL && root->right != NULL) 
return sum(root->left, val * 10 + root->val) + sum(root->right, val * 10 + root->val);
}
};