leetcode 589. N-ary Tree Preorder Traversal

一题目

Given 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).

 

Follow up:

Recursive solution is trivial, could you do it iteratively?

 

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

二 分析

   N叉树的前序遍历。刚听完覃超老师讲的二叉树。

所以成热打铁练习下easy级别的。

就是采用递归的方式：先根，再从左到右遍历子节点。

 public List preorder(Node root) {
        if (root != null){
           list.add(root.val);
            for(int i=0;i< root.children.size();i++ ) {
                preorder(root.children.get(i));
            }
        }
        return list;
    }