N-ary Tree Level Order Traversal

Description

Given an n-ary tree, return the level order 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],[3,2,4],[5,6]]

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

 

Constraints:

• The height of the n-ary tree is less than or equal to 1000
• The total number of nodes is between [0, 10^4]

Solution(javascript)

/**
 * // Definition for a Node.
 * function Node(val,children) {
 *    this.val = val;
 *    this.children = children;
 * };
 */
/**
 * @param {Node} root
 * @return {number[][]}
 */
const levelOrder = (root) => {
  const res = []
  if (!root) {
    return res
  }
  let frontier = [root]
  while (frontier.length) {
    const next = []
    res.push(frontier.map(node => node.val))
    frontier.forEach((node) => {
      if (node.children) {
        next.push(...node.children)
      }
    })
    frontier = next
  }
  return res
}