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 a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */

int DFS(struct TreeNode *curNode, int curSum){
    int leftSum = 0;
    int rightSum = 0;
    curSum += curNode->val;
    if(curNode->left == NULL && curNode->right == NULL)
        return curSum;
    if(curNode->left != NULL)
        leftSum = DFS(curNode->left, 10 * curSum);
    if(curNode->right != NULL)
        rightSum = DFS(curNode->right, 10 * curSum);
    return leftSum + rightSum;
}
int sumNumbers(struct TreeNode* root) {
    // dfs, go deep until to leaf
    int sum = 0;
    if(root == NULL)
        return 0;
    return DFS(root, 0);
}