Algorithm
Problem Name: 589. N-ary Tree Preorder Traversal
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.
Code Examples
#1 Code Example with Java Programming
Code -
Java Programming
class Solution {
public List preorder(Node root) {
if (root == null) {
return new ArrayList<>();
}
List < Integer> list = new ArrayList<>();
Stack stack = new Stack<>();
stack.push(root);
while (!stack.isEmpty()) {
Node popped = stack.pop();
list.add(popped.val);
List < Node> children = popped.children;
for (int i = children.size() - 1; i >= 0; i--) {
stack.push(children.get(i));
}
}
return list;
}
}
Input
root = [1,null,3,2,4,null,5,6]
Output
[1,3,5,6,2,4]
#2 Code Example with Javascript Programming
Code -
Javascript Programming
const preorder = function(root) {
const arr = []
traverse(root, arr)
return arr
};
function traverse(node, arr) {
if(node === null) return
arr.push(node.val)
for(let i = 0; i < node.children.length; i++) {
traverse(node.children[i], arr>
}
}
Input
root = [1,null,3,2,4,null,5,6]
Output
[1,3,5,6,2,4]
#3 Code Example with C# Programming
Code -
C# Programming
using System.Collections.Generic;
namespace LeetCode
{
public class _0589_NAryTreePreorderTraversal
{
public IList < int> Preorder(Node root)
{
var result = new List<int>();
if (root == null) return result;
var stack = new Stack < Node>();
stack.Push(root);
while (stack.Count > 0)
{
var node = stack.Pop();
result.Add(node.val);
if (node.children != null)
for (int i = node.children.Count - 1; i >= 0; i--)
stack.Push(node.children[i]);
}
return result;
}
public class Node
{
public int val;
public IList < Node> children;
public Node() { }
public Node(int _val)
{
val = _val;
}
public Node(int _val, IList < Node> _children)
{
val = _val;
children = _children;
}
}
}
}
Input
root = [1,null,3,2,4,null,5,6]
Output
[1,3,5,6,2,4]