# Leetcode Sum Root to Leaf Numbers Java Solution

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.

Note: A leaf is a node with no children.

Example:

```Input: [1,2,3]
1
/ \
2   3
Output: 25
Explanation:
The root-to-leaf path `1->2` represents the number `12`.
The root-to-leaf path `1->3` represents the number `13`.
Therefore, sum = 12 + 13 = `25`.```

Example 2:

```Input: [4,9,0,5,1]
4
/ \
9   0
/ \
5   1
Output: 1026
Explanation:
The root-to-leaf path `4->9->5` represents the number 495.
The root-to-leaf path `4->9->1` represents the number 491.
The root-to-leaf path `4->0` represents the number 40.
Therefore, sum = 495 + 491 + 40 = `1026`.```

Solution Using DFS:
We will DFS(Depth First Search) to find the numbers and add them to the sum, the time complexity would be O(N).

``````class HackerHeap {
public int sumNumbers(TreeNode root) {
if (root == null) return 0;
return dfs(root, 0, 0);
}
public int dfs(TreeNode node, int num, int sum) {
if(node == null) return sum;
num = num*10 + node.val;
if(node.left == null && node.right == null) {
return sum+=num;
}
return dfs(node.left, num, sum) + dfs(node.right, num, sum);
}
}
``````

In this video explanation we will solve Leetcode Sum Root to Leaf Numbers Java Solution