Solution of hackerrank Binary Tree Nodes question - sql

Question

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:
why below solution is not working :
select n,
CASE when P is null then 'Root'
when (select count(*) from BST where n = p)>0 then 'Inner'
else 'Leaf'
end as nodetype from BST
order by n
and below solution is working:
select n,
CASE when P is null then 'Root'
when (select count(*) from BST where b.n = p)>0 then 'Inner'
else 'Leaf'
end as nodetype from BST b
order by n

Answer 1

In your fist query you are comparing n with p column within the subquery which should never be true.
In second query you are comparing n column of outer query with p column of subquery which will return more than 0 if there is at least one leaf under the b.n node otherwise it will return 0.

Answer 2

Using a case statement is a way to go. However, to determine if a node is 'Inner' one needs to see if it is a parent to another node i.e. is its value N in the set of all P values.
SELECT N, CASE
WHEN P IS NULL THEN 'Root'
WHEN N IN (SELECT P FROM BST) THEN 'Inner'
ELSE 'Leaf' END as node_type FROM BST ORDER BY N

Answer 3

By using below code, you can easily solve the binary tree nodes question.In foreach statement we can check the max value and print in console
int n = Convert.ToInt32(Console.ReadLine().Trim());
string[] groupings = Convert.ToString(n, 2).Split("0");
int max = 0;
foreach(string s in groupings){
if(max < s.Length){
max = s.Length;
}
}
Console.WriteLine(max);