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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?

How the tests work: the tree is written in level order with null closing each group of children — [1,null,3,2,4,null,5,6]. Your function receives real Node objects.

TypeScript
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List of test cases (12)
Case 1
root = [1,null,3,2,4,null,5,6]
Case 2
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]
Case 3
root = []
Case 4
root = [1]
Case 5
root = [1,null,2,3,4]
Case 6
root = [1,null,2,null,3,null,4,null,5]
Case 7
root = [10,null,20,30]
Case 8
root = [5,null,3,6,2,null,1,4]
Case 9
root = [1,null,2,3,4,5,null,null,6,7,null,8]
Case 10
root = [42,null,1,2,3,4,5]
Case 11
root = [7,null,8,9,10,null,11,null,12,null,13]
Case 12
root = [0,null,1,2,null,3,4,null,5]