[MySQL/HackerRank] Binary Tree Nodes

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

Binary Tree Nodes | HackerRank

문제

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.

Code

SELECT N, CASE WHEN P IS NULL THEN 'Root'
                WHEN N NOT IN (SELECT DISTINCT P FROM BST WHERE P IS NOT NULL) THEN 'Leaf'
                ELSE 'Inner' END
FROM BST
ORDER BY N