0590-n-ary-tree-postorder-traversal.js

// 590. N-ary Tree Postorder Traversal
// Easy   71%


// Given 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).

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

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


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

/**
 * @param {Node} root
 * @return {number[]}
 */
const postorder = function(root) {
  if (root === null) return []
  const res = []
  function postorder(node) {
    for (let c of node.children) postorder(c)
    res.push(node.val)
  }
  postorder(root)
  return res
}

;[
  [1,null,3,2,4,null,5,6],
].forEach(() => {

})

// Solution:
// 1. 后序遍历，递归
// 2. 使用栈
// TODO: #590 多叉树的构造函数

// Submission Result: Accepted