---
title: 'Rendez-vous with cassidoo #200, interview question of the week'
url: 'https://www.trancart.eu/en/blog/20210618-rendezvous-cassidoo-200'
markdown: 'https://www.trancart.eu/en/blog/20210618-rendezvous-cassidoo-200.md'
lang: en
date: '2021-06-18'
description: "I've recently discovered Cassidy's newsletter, more precisely this one and really liked it: it's short it's fun and there is a fun interview question I admit I haven't read the linked articles :-) This week’s question: Given a direction and a number of columns, write a function that outputs an a…"
taxonomy:
  tag:
    - cassidoo
    - sql
    - puzzle
---

# Rendez-vous with cassidoo #200, interview question of the week

I've recently discovered [Cassidy's newsletter](https://cassidoo.co/newsletter/), more precisely [this one](https://buttondown.email/cassidoo/archive/there-will-always-be-enemies-time-to-stop-being/) and really liked it:

- it's short
- it's fun
- and there is a fun interview question

I admit I haven't read the linked articles :-)

## This week’s question:

> Given a direction and a number of columns, write a function that outputs an arrow of asterisks (see the pattern in the examples below)!
> 
> Example:
> 
> ```
> $ printArrow('right', 3)
> Output:
> *
>  *
>   *
>  *
> *
> 
> $ printArrow('left', 5)
> Output:
>     *
>    *
>   *
>  *
> *
>  *
>   *
>    *
>     *
> ```

## My solution

I've decided to do it in SQL (PostgreSQL flavour) because these times it's the language I have the most fun with for these little puzzles.

My solution is based on 2 main ideas:

- `generate_series` to generate the lines (it's kind of obvious if you're used to do these puzzles in SQL)
- it looks like an `abs` function plot

```sql
CREATE OR REPLACE FUNCTION public.print_arrow(
        direction text, 
        columnnumber integer)
 RETURNS text
 LANGUAGE sql
 IMMUTABLE
AS $function$
  select 
    -- we repeat a space s times, add a * at the end 
    -- and separate lines with \n
    -- nothing surprising...
    string_agg(repeat(' ', s) || '*', E'\n')
  from (
    -- here is the number of space computation
    select
      case
        when direction = 'right' then 
            columnnumber - abs(line  - columnnumber) - 1
        when direction = 'left' then 
            abs(line - columnnumber)
        else /*uh oh!*/ 0
      end as s
    from 
      -- generate numbers from 1 to 2n-1
      generate_series(1, 2 * columnnumber - 1) line
  ) spaces;
$function$
```

Not very complicated, but fun to see that SQL gives us everything we need in this case.

([Photo](https://www.pexels.com/photo/never-stop-exploring-signboard-954662/) by Dale Brooks from Pexels.)

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