129. Sum Root to Leaf Numbers(Tree; DFS)

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.

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