LeetCode_129 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.

int sum = 0;
public int sumNumbers(TreeNode root) {
if(root == null) return sum;

dfs(root, root.val);
return sum;
}
private void dfs(TreeNode root, int num){
if(root == null) return;

if(root.left == null&& root.right==null)sum +=num;
if (root.left !=null) {
dfs(root.left, num*10+root.left.val);
}
if (root.right != null) {
dfs(root.right, num*10+root.right.val);
}
}