# Introduction

Recently, me and a couple of my friends decided to play some cards, and one of them suggested the game 'Irish Snap', which was the inspiration for this challenge. However, I later learnt that the game has a lot of different rules that you can play with, some of which are listed here. The rules that are in this challenge aren't currently listed on that page, hence the name, 'Variant Rules'

# The Challenge

Given an array of 3 cards, output a truthy or falsey value depending on if they make a valid snap in a game of Irish snap.

# Input

The input will be an array of 3 numbers, ranging from 1-13 inclusive, with 1 representing an ace, 11 representing a jack, 12 representing a queen and 13 representing a king. The input can be in any order of top, middle, bottom.

# Rules

The 4 different criteria for if cards make an Irish snap are:

• The top and middle cards are the same
• The top and middle cards have a difference of one
• The top and bottom cards are the same
• The top and bottom cards have a difference of one

If any of these criteria are met, you must output a truthy value. As well as this, for the two criteria that require the cards to have a difference of one, it 'wraps around', meaning that an ace and a king are considered to have a difference of one, and vice versa.

# Test Cases

Input (Bottom, Middle, Top) -> Output
1 13 7 -> False
1 4 13 -> True
9 3 6 -> False
8 9 7 -> True
2 6 5 -> True
12 5 11 -> True
10 4 8 -> False
12 13 7 -> False
9 7 10 -> True
7 3 1 -> False
4 2 3 -> True

• Can we take the cards seperately? Or take input as top, [middle, bottom]?
– Jo King
Aug 22, 2019 at 12:52
• sure, you can do both. changed the question to reflect that Aug 22, 2019 at 12:54
• Can we invert the output, i.e return False for valid snaps and vice versa? How about a test case where both middle and bottom are valid?
– Jo King
Aug 22, 2019 at 13:11
• Yeah, you can invert the output. Also, added that test case Aug 22, 2019 at 13:14
• Must the output values be consistent or could we, for example, output 0 for false and any other integer for true or, even, any negative integer for false or any positive integer for true? Aug 22, 2019 at 23:11

# Python 3, 38 bytes

lambda x,y,z:{x-y,x-z}&{0,1,12,-1,-12}


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Returns a non-empty set (truthy) if valid, empty set (falsey) if not. Takes input in order top-middle-bottom, but can be rearranged for same code size.

# Perl 6, 16 bytes

3>(*-(*|*)+1)%13


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Anonymous whatever lambda that takes input as top, middle, bottom and returns a Junction that evaluates to True or False

• Too bad whitespace is required before <, this was the perfect chance to have a heart smiley. Aug 22, 2019 at 13:18

# 05AB1E, 7 6 bytes

α12%ß!


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Takes inputs as [middle, bottom], top.

α        # absolute difference
12%     # mod 12
ß    # minimum
!   # factorial


Only 1 is truthy in 05AB1E. 0! and 1! are both 1, while no other number has a factorial of 1.

# J, 12 bytes

1 e.2>12||@-


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Taking bottom middle as left arg, top as right arg.

# J, 24 bytes

1 e.2>#:@3 5(12||@-/)@#]


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• #:@3 5 The numbers 3 and 5 in binary are 0 1 1 and 1 0 1 which are the masks for the middle/top and bottom/top cards respectively
• (12||@-/)@# We filter the input with those masks, take the abs value of the resulting differences, then the remainder when divided by 12 (for the ace-king case)
• 1 e.2> are either of the resulting numbers less than 2, ie, 0 or 1?

# JavaScript (ES6), 29 bytes

Takes input as ([bottom, middle])(top).

The output is inverted.

a=>c=>a.every(n=>(n-c)/2%6|0)


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# JavaScript (ES6),  37  30 bytes

Saved 1 byte thanks to @Grimy

Takes input as ([bottom, middle])(top).

a=>c=>a.some(n=>(n-=c)*n%72<2)


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• %144 could be %72 Aug 22, 2019 at 13:08
• @Grimy Thanks! FWIW, %13 would also work. Aug 22, 2019 at 13:34

# Charcoal, 12 bytes

›²⌊﹪↔⁻Ｅ²ＮＮ¹²


Try it online! Port of @Grimy's answer. Takes input as three separate values bottom, middle, top, and outputs using Charcoal's default Boolean format of - for true, nothing for false. Explanation:

 ²              Literal 2
›               Is greater than
⌊             Minimum of
↔            Absolute value of (vectorised)
Ｅ²Ｎ       First two numeric inputs as a list ([bottom, middle])
⁻          Minus (vectorised)
Ｎ      Third input (top)
﹪            Modulo (vectorised)
¹²    Literal 12


# Perl 5-ap, 31 bytes

$t=<>}{$\|=abs($t-$_)%12<2for@F


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### Input:

bottom middle
top


Actually, the order of the middle and bottom doesn't matter.

### Output:

0 for false; 1 for true

# Pyth, 12 11 bytes

Takes input as [bottom, top, middle] or [middle, top, bottom] (both work). Outputs [] (Falsy in Pyth) if there's no valid snap, a non-empty array otherwise.

f>2%.aT12.+


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If a consistent truthy/falsy value is required, add .A in front for +2 bytes. Then output will be True or False.

## Explanation

  f             # Filter on lambda T:
>2           # 2 >
.aT       #     abs(T)
%   12     #            % 12
.+   # the list of deltas (difference between consecutive elements)

.A (if required)# Any truthy values in the above list?


Edit: -1 with a different approach

# Jelly, 6 bytes

ạ%12ṠƑ


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# C (gcc), 47 43 bytes

f(b,m,t){return(1<<t-m|1<<t-b)&0x80101003;}


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# Japt, 7 bytes

d_aV <2


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# Jelly, 6 bytes

I%12ỊẸ


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A monadic link taking the list of [middle, top, bottom] as its argument and returning 1 for snap and 0 for no snap.

# T-SQL 2008, 40 bytes

PRINT 1/-~abs((@-@2)%12/2*((@-@3)%12/2))


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# [R], 23 bytes

takes input as a=c(bottom,top,middle):

any(abs(diff(a))%%12<2)