LeetCode in Kotlin
589. N-ary Tree Preorder Traversal
Easy
Given the root of an n-ary tree, return the preorder traversal of its nodes’ values.
Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)
Example 1:
Input: root = [1,null,3,2,4,null,5,6]
Output: [1,3,5,6,2,4]
Example 2:
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [1,2,3,6,7,11,14,4,8,12,5,9,13,10]
Constraints:
- The number of nodes in the tree is in the range
[0, 104]. 0 <= Node.val <= 104- The height of the n-ary tree is less than or equal to
1000.
Follow up: Recursive solution is trivial, could you do it iteratively?
Solution
import com_github_leetcode.Node
/*
* Definition for a Node.
* class Node(var `val`: Int) {
* var children: List<Node?> = listOf()
* }
*/
class Solution {
fun preorder(root: Node?): List<Int> {
val res: MutableList<Int> = ArrayList()
preorderHelper(res, root)
return res
}
private fun preorderHelper(res: MutableList<Int>, root: Node?) {
if (root == null) {
return
}
res.add(root.`val`)
for (node in root.neighbors) {
preorderHelper(res, node)
}
}
}