easy

N-ary Tree Preorder Traversal

To solve this problem, we can use a recursive approach to perform a preorder traversal of the n-ary tree. In a preorder traversal, we first visit the current node, then recursively visit each of its children from left to right.

Here is the Javascript code that implements the above algorithm:

function preorder(root) {
  const result = [];
  if (!root) {
    return result;
  }
  result.push(root.val);
  for (let i = 0; i < root.children.length; i++) {
    result.push(...preorder(root.children[i]));
  }
  return result;
}

The function preorder takes in the root node of the n-ary tree and returns an array of integers representing the preorder traversal of the tree.

The first thing we do in the function is create an empty array result to store the preorder traversal.

Next, we check if the root node is null. If it is null, we return the result array.

If the root node is not null, we add its value (root.val) to the result array.

We then iterate through the children of the root node using a for loop. For each child, we recursively call the preorder function and concatenate its result to the result array using the spread operator (...).

Finally, we return the result array.

The time complexity of this algorithm is O(n), where n is the total number of nodes in the n-ary tree. This is because we need to visit each node exactly once during the preorder traversal. The space complexity is also O(n), because we need to store the preorder traversal in an array of size n. However, the actual space used by the function call stack is O(h), where h is the height of the n-ary tree. This is because the function calls are recursive and the maximum depth of the function call stack is equal to the height of the tree.