[HackerRank] Binary Tree Nodes

https://www.hackerrank.com/challenges/binary-search-tree-1/problem?isFullScreen=true 

Binary Tree Nodes | HackerRank

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You are given a table, BST, containing two columns: N and P, where N represents the value of a node in Binary Tree, and P is the parent of N.

Write a query to find the node type of Binary Tree ordered by the value of the node. Output one of the following for each node:

• Root: If node is root node.
• Leaf: If node is leaf node.
• Inner: If node is neither root nor leaf node.

Sample Input

Sample Output

1 Leaf

2 Inner

3 Leaf

5 Root

6 Leaf

8 Inner

9 Leaf

Explanation

The Binary Tree below illustrates the sample:

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[My Answer]

 

SELECT 
N, 
(case when P is null then 'Root'
when N in (select P from BST) then 'Inner'
else 'Leaf' end) node_type
FROM BST AS B 
ORDER BY N

문제 이해만 빨리되면 금방 할수있겠다.