Add baffling-birthdays exercise

[resu-xuniL]

Add baffling-birthdays exercice to track.
I change difficulty from 1 to 4.

Hope everything is correct.

float with bash !
I increase the tolerance for the exercice with 10 and 23 people because, after multiple runs (many time consuming), sometimes one or the other fail when checking only respectively 11|12|13 and 50|51|52.
or might be another way to do it more precisely ?

The other option is to increase the number of runs, but this is very time consuming in bash! (set now at 1000)
maybe I can try to parallelize the computings? or creating a file would help?

I got these result while debbuging :

   (from function `assert_output' in file bats-extra.bash, line 394,
    in test file baffling_birthdays.bats, line 162)
     `assert_output $expect' failed
   
   -- output differs --
   expected : 11.694818
   actual   : 12.70
   --
   
 ✗ estimated probability of at least one shared birthday -> among twenty-three people
   (from function `assert_output' in file bats-extra.bash, line 394,
    in test file baffling_birthdays.bats, line 170)
     `assert_output $expect' failed
   
   -- output differs --
   expected : 50.729723
   actual   : 51.10
   --
   
 ✗ estimated probability of at least one shared birthday -> among seventy people
   (from function `assert_output' in file bats-extra.bash, line 394,
    in test file baffling_birthdays.bats, line 178)
     `assert_output $expect' failed
   
   -- output differs --
   expected : 99.915958
   actual   : 99.90
   --```
---

Reviewer Resources:

[Track Policies](https://github.com/exercism/bash/blob/master/POLICIES.md)

[resu-xuniL]

23 persons test failed again...
I'll work on it. Any suggestions are welcome! ^^
it passed just before the this test ...

[IsaacG]

Geez... 23 persons test failed again... I'll work on it tomorrow. Any suggestions are welcome! ^^ it passed just before the this test ...

You can try doubling your runs from 1k to 2k. You can try widening the acceptable probability range.

[resu-xuniL]

OK, it passes 6 times in a row (with this one) so far...
Thank you for your help!
(with runs at 1500)

[resu-xuniL]

It passed 4 times in a row before i push this, and now it failed for 10 and 23 people tests!
shall i increase back the tolerence (i decreased them)? or increase the runs to 3k ?

(in the php track, I ran it 10k ... but in bash it would take so much time !!)

[resu-xuniL]

re-increased tolerance for 23 people test.

[IsaacG]

(in the php track, I ran it 10k ... but in bash it would take so much time !!)

How much time is too much time? How slow is 3k? 4k?

If it takes more than, say, 5 seconds, we probably want to widen the tolerance.

[resu-xuniL]

(in the php track, I ran it 10k ... but in bash it would take so much time !!)

How much time is too much time? How slow is 3k? 4k?

If it takes more than, say, 5 seconds, we probably want to widen the tolerance.

it was about 20+ minutes for 2k - 3k before modifications...

[glennj]

Regarding the slowness, you'll get must faster performance by using the builtin $RANDOM variable instead of calling out to shuf

# return a random number in the range 0 <= n < $1
random_int() {
    echo $(( RANDOM % $1 ))
}
february_days=$(( 1 + $(random_int 28) ))

With group_size = 10 and runs = 5000, you're calling shuf 150,000 times and date 50,000 times.

[resu-xuniL]

I don't think this is 'hoops', this is just that I need learning more and more :)

[resu-xuniL]

new stats with runs=2k

      1 x 9
     12 x 10
     65 x 11
     40 x 12
      8 x 13

      1 x 47
      5 x 48
     15 x 49
     28 x 50
     25 x 51
     11 x 52
      3 x 53

[IsaacG]

The fact that this requires so much work and learning to get working in a reasonable amount of time indicates to me that this may not be a great fit for the bash track 😄

Thoughts on marking this foregone, @glennj ?

[glennj]

The fact that this requires so much work and learning to get working in a reasonable amount of time indicates to me that this may not be a great fit for the bash track 😄

Thoughts on marking this foregone, @glennj ?

We have:

1. a monte-carlo approach that takes an unreasonable amount of time,
2. a monte-carlo approach that is reasonable, and
3. non-randomized mathematical approaches (not demonstrated here, but https://exercism.org/tracks/lua/exercises/baffling-birthdays/solutions has some)

I think we can proceed. We'll probably see monstly 1 and 3 submitted.

An instructions.append.md file would be useful to gently steer people along. Approaches articles might help too.

[IsaacG]

I think we can proceed. We'll probably see monstly 1 and 3 submitted.

An instructions.append.md file would be useful to gently steer people along. Approaches articles might help too.

Solutions that take long to run will fail the test runner. The approaches article can only be viewed after passing tests.

We'd want to provide a fair bit of guidance in the append file to help students get this to pass on the test runner.

[glennj]

How about this approach:

1. add "status": "wip" to the exercise blob in config.json and we merge this PR.
2. then we work on a new PR to add .docs/instructions.append.md and change the status to "beta".

[IsaacG]

What's the status on this PR?

[glennj]

@IsaacG I think this is ready to merge. The exercise status is "wip".

[resu-xuniL]

fixes at #893