589. N-ary Tree Preorder Traversal LeetCode Solution

In this guide, you will get 589. N-ary Tree Preorder Traversal LeetCode Solution with the best time and space complexity. The solution to N-ary Tree Preorder Traversal problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Problem Statement
Complexity Analysis
N-ary Tree Preorder Traversal solution in C++
N-ary Tree Preorder Traversal solution in Java
N-ary Tree Preorder Traversal solution in Python
Additional Resources

589. N-ary Tree Preorder Traversal LeetCode Solution image

Problem Statement of 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.

Follow up: Recursive solution is trivial, could you do it iteratively?

Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(n)

589. N-ary Tree Preorder Traversal LeetCode Solution in C++

class Solution {
 public:
  vector<int> preorder(Node* root) {
    if (root == nullptr)
      return {};

    vector<int> ans;
    stack<Node*> stack{{root}};

    while (!stack.empty()) {
      root = stack.top(), stack.pop();
      ans.push_back(root->val);
      for (auto it = root->children.rbegin(); it != root->children.rend(); ++it)
        stack.push(*it);
    }

    return ans;
  }
};
/* code provided by PROGIEZ */

589. N-ary Tree Preorder Traversal LeetCode Solution in Java

class Solution {
  public List<Integer> preorder(Node root) {
    if (root == null)
      return new ArrayList<>();

    List<Integer> ans = new ArrayList<>();
    Deque<Node> stack = new ArrayDeque<>();
    stack.push(root);

    while (!stack.isEmpty()) {
      root = stack.pop();
      ans.add(root.val);
      for (int i = root.children.size() - 1; i >= 0; --i)
        stack.push(root.children.get(i));
    }

    return ans;
  }
}
// code provided by PROGIEZ