[LeetCode] 590. N-ary Tree Postorder Traversal_Easy

Posted 2020-12-24

Given an n-ary tree, return the postorder traversal of its nodes\' values.

 

For example, given a 3-ary tree:

 

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

 

这个题目思路就是跟LeetCode questions conlusion_InOrder, PreOrder, PostOrder traversal里面postorder traversal很像, 只是将left child 和right child变成了children而已,

当然这里假设的是children的顺序是从左到右的.

 

code

1) recursive

class Solution:
    def naryPostOrderTraversal(self, root):
        def helper(root):
            if not root: return
            for each in root.children:
                helper(each)
            ans.append(root.val)
        ans = []
        helper(root)
        return ans

 

2) iterable

class Solution:
    def naryPostOrderTraversal(self, root):
        if not root: return []
        stack, ans = [(root, False)], []
        while stack:
            node, visited  = stack.pop()
            if visited:
                ans.append(node.val)
            else:
                stack.append((node, True))
                for each in node.children[::-1]:
                    stack.append((each, False))
        return ans