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euclidean algorithm in crystal #887

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37 changes: 37 additions & 0 deletions contents/euclidean_algorithm/code/crystal/euclidean.cr
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Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
def euclid_mod(a : Int, b : Int)
a = a.abs
b = b.abs

loop do
b, a = a % b, b
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If b is already zero trying to do a % b throws DivisionByZeroError. This could be fixed by breaking before this line, or using while instead of loop

break if b == 0
end

return a
end

def euclid_sub(a : Int, b : Int)
a = a.abs
b = b.abs

loop do
if a > b
a -= b
else
b -= a
end
break if a == b
end
Comment on lines +17 to +24
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This goes into an infinite loop if a is equal to b. Moving the break to happen before the if would fix the issue, but I think even better would be to use a while loop instead:

while a != b
  if a > b
    a -= b
  else
    b -= a
  end
end


return a
end

def main
euc_mod = euclid_mod(64 * 67, 64 * 81)
euc_sub = euclid_sub(128 * 12, 128 * 77)

puts "Modulus-based euclidean algorithm result: #{euc_mod}"
puts "Subtraction-based euclidean algorithm result: #{euc_sub}"
end

main
6 changes: 6 additions & 0 deletions contents/euclidean_algorithm/euclidean_algorithm.md
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Expand Up @@ -83,6 +83,8 @@ The algorithm is a simple way to find the *greatest common divisor* (GCD) of two
[import:1-14, lang="powershell"](code/powershell/euclidean_algorithm.ps1)
{% sample lang="coco" %}
[import:1-9, lang="coconut"](code/coconut/euclidean.coco)
{% sample lang="crystal" %}
[import:13-27, lang="crystal"](code/crystal/euclidean.cr)

{% endmethod %}

Expand Down Expand Up @@ -173,6 +175,8 @@ Modern implementations, though, often use the modulus operator (%) like so
[import:16-27, lang="powershell"](code/powershell/euclidean_algorithm.ps1)
{% sample lang="coco" %}
[import:12-15, lang="coconut"](code/coconut/euclidean.coco)
{% sample lang="crystal" %}
[import:1-11, lang="crystal"](code/crystal/euclidean.cr)

{% endmethod %}

Expand Down Expand Up @@ -290,6 +294,8 @@ The code snippets were taken from this [Scratch project](https://scratch.mit.edu
[import, lang="powershell"](code/powershell/euclidean_algorithm.ps1)
{% sample lang="coco" %}
[import, lang="coconut"](code/coconut/euclidean.coco)
{% sample lang="crystal" %}
[import, lang="crystal"](code/crystal/euclidean.cr)

{% endmethod %}

Expand Down