[HackerRank SQL] Binary Tree Nodes

www.hackerrank.com/challenges/binary-search-tree-1/problem

Binary Tree Nodes | HackerRank

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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Answer

select 
    N,
    case when p is null  then 'Root' #Root 는 p(parent)가 없다(null)
        when N in (select P from BST) then 'Inner'  # root도 아니고 P에도 포함된다면 inner이다.
        else 'Leaf'
        end
from BST
order by N

 

Result