589. N-ary Tree Preorder Traversal

QUESTION:

Given an n-ary tree, return the preorder traversal of its nodes’ values.

For example, given a 3-ary tree:

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Return its preorder traversal as: [1,3,5,6,2,4].

Note:

Recursive solution is trivial, could you do it iteratively?

EXPLANATION:

就是一个DFS的算法，深度优先的遍历，只要学过树的结构的其实都是很容易的。

SOLUTION:

class Solution {
    List<Integer> preorderResult = new ArrayList<>();
    public List<Integer> preorder(Node root) {
        if(root == null) return new ArrayList<>();
        preorderResult.add(root.val);
        for(int i =0;i<root.children.size();i++){
            preorder(root.children.get(i));
        }
        return preorderResult;
    }
}
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