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N-ary Tree Postorder Traversal

Problem statement​

Given the root of an n-ary tree, return the postorder 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: [5,6,3,2,4,1]

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: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]

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?

My solution​

/**
 * // Definition for a Node.
 * function Node(val,children) {
 *    this.val = val;
 *    this.children = children;
 * };
 */

/**
 * @param {Node|null} root
 * @return {number[]}
 */
var postorder = function(root) {
    if (!root) {
        return [];
    }
    
    let stack = [root];
    let postOrderVal = []
    
    while (stack.length) {
        const node = stack.pop();
        postOrderVal.unshift(node.val);
        
        for (const child of node.children) {
            stack.push(child)
        }
    }
    
    return postOrderVal;
};