I have been following the series of posts written by my friend and SQL MCM Wayne Sheffield on some TSQL puzzles – these puzzles are from a guy named Eric Wastl and called ‘Advent of Code‘.
Your challenge basically after you sign up is to solve a series of puzzles arranged in the form of a christmas tree – each puzzle has two parts to it, the second part will be revealed after the first part is successfully solved. While the fundamental puzzle is the same, each person will be presented with a different data set for solving it, so no two people get the same answer. You can paste your answer in and verify it for correctness. These puzzles are not TSQL/SQL Server specific, but TSQL lends itself beautifully well to solving them.
I took up the challenge and came up with my own answers – Day 1 as below:
Part 1 of puzzle:
Santa is trying to deliver presents in a large apartment building, but he can’t find the right floor – the directions he got are a little confusing. He starts on the ground floor (floor 0) and then follows the instructions one character at a time.
An opening parenthesis, (, means he should go up one floor, and a closing parenthesis, ), means he should go down one floor.
The apartment building is very tall, and the basement is very deep; he will never find the top or bottom floors.
For example:
(())and()()both result in floor0.(((and(()(()(both result in floor3.))(((((also results in floor3.())and))(both result in floor-1(the first basement level).)))and)())())both result in floor-3.
To what floor do the instructions take Santa? I am supplied with the string of braces as my data.
Solution :
DECLARE @leftbrace CHAR(1), @rightbrace CHAR(1)
DECLARE @string VARCHAR(MAX)
SET @string = 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SET @leftbrace = '('
SET @rightbrace = ')'
SELECT (LEN(@string) - LEN(REPLACE(@string, @rightbrace, ''))) - (LEN(@string) - LEN(REPLACE(@string, @leftbrace, '')))
Easy peasy right? My answer was 280. Now harder..onto part 2
Part 2 : Now, given the same instructions, find the position of the first character that causes him to enter the basement (floor -1). The first character in the instructions has position 1, the second character has position 2, and so on.
For example:
)causes him to enter the basement at character position1.()())causes him to enter the basement at character position5.
What is the position of the character that causes Santa to first enter the basement?
This gets much harder..well sort of..it is easy to do character by character, the RBAR way, although you are parsing a variable here and that might be excusable given how TSQL works generally with this..but a better way perhaps would be to parse the string using a recursive CTE – as below. My answer was 1797. I had fun doing this as i had not parsed a variable this way and learnt how. I hope you do too..and do remember, your set of data is different , so don’t make the same mistake I did (cut and paste from here and wonder why the site is not accepting your answer!!).
Happy Coding Fun and for the next part, next week!
DECLARE @start INT, @end INT, @pos INT
DECLARE @leftbrace CHAR(1)
SET @leftbrace = '(';
SET @string = 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SET @start = 1
SET @pos = 0;
WITH a AS (SELECT [start] = 1, [end] = LEN(@string), [pos] = IIF(SUBSTRING(@string, @start, 1) = @leftbrace, @pos + 1, @pos - 1) UNION ALL SELECT [start] = [start] + 1, [end] = LEN(@string), [pos] = IIF(SUBSTRING(@string, [start]+1, 1) = @leftbrace, [pos] + 1, [pos] - 1) FROM a WHERE [start] <= [end])
SELECT TOP(1) [start] FROM a WHERE pos = -1 OPTION (MAXRECURSION 0)