HackerRank-AdvancedSelect-Binary Tree Nodes

Binary Tree Nodes

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:

My solution

SELECT DISTINCT(bst1.N), CASE WHEN bst1.P IS NULL THEN 'Root'
            WHEN bst2.N IS NULL THEN 'Leaf'
            ELSE 'Inner'
            END
FROM BST bst1 LEFT OUTER JOIN BST bst2
ON bst1.N=bst2.P
ORDER BY bst1.N ASC;

Most vote solution

SELECT N, CASE WHEN P IS NULL THEN 'Root'
               WHEN N IN (SELECT DISTINCT(P) FROM BST) THEN 'Inner'
               ELSE 'Leaf'
          END
FROM BST
ORDER BY N;