cr

crystal/hamming/README.md

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+# Hamming
+
+Calculate the Hamming difference between two DNA strands.
+
+A mutation is simply a mistake that occurs during the creation or
+copying of a nucleic acid, in particular DNA. Because nucleic acids are
+vital to cellular functions, mutations tend to cause a ripple effect
+throughout the cell. Although mutations are technically mistakes, a very
+rare mutation may equip the cell with a beneficial attribute. In fact,
+the macro effects of evolution are attributable by the accumulated
+result of beneficial microscopic mutations over many generations.
+
+The simplest and most common type of nucleic acid mutation is a point
+mutation, which replaces one base with another at a single nucleotide.
+
+By counting the number of differences between two homologous DNA strands
+taken from different genomes with a common ancestor, we get a measure of
+the minimum number of point mutations that could have occurred on the
+evolutionary path between the two strands.
+
+This is called the 'Hamming distance'.
+
+It is found by comparing two DNA strands and counting how many of the
+nucleotides are different from their equivalent in the other string.
+
+    GAGCCTACTAACGGGAT
+    CATCGTAATGACGGCCT
+    ^ ^ ^  ^ ^    ^^
+
+The Hamming distance between these two DNA strands is 7.
+
+# Implementation notes
+
+The Hamming distance is only defined for sequences of equal length. This means
+that based on the definition, each language could deal with getting sequences
+of equal length differently.
+
+## Setup
+
+Follow the setup instructions for Crystal here:
+
+http://exercism.io/languages/crystal
+
+More help installing can be found here:
+
+http://crystal-lang.org/docs/installation/index.html
+
+## Making the Test Suit Pass
+
+Execute the tests with:
+
+```bash
+$ crystal spec
+```
+
+In each test suite all but the first test have been skipped.
+
+Once you get a test passing, you can unskip the next one by changing `pending` to `it`.
+
+## Source
+
+The Calculating Point Mutations problem at Rosalind [http://rosalind.info/problems/hamm/](http://rosalind.info/problems/hamm/)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

crystal/hamming/spec/hamming_spec.cr

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+require "spec"
+require "../src/*"
+
+describe "Hamming" do
+  describe "#compute" do
+    it "computes no difference for identical single nucleotide strands" do
+      Hamming.compute("A", "A").should eq 0
+    end
+
+    pending "computes a distance for single nucleotide strands" do
+      Hamming.compute("A", "G").should eq 1
+    end
+
+    pending "computes a distance for small strands" do
+      Hamming.compute("AG", "CT").should eq 2
+    end
+
+    pending "computes a distance for medium strands" do
+      Hamming.compute("GGACG", "GGTCG").should eq 1
+    end
+
+    pending "computes a distance for large strands" do
+      Hamming.compute("GGACGGATTCTG", "AGGACGGATTCT").should eq 9
+    end
+
+    pending "raises an exception when strands aren't of equal length" do
+      expect_raises(ArgumentError) { Hamming.compute("GCC", "A") }
+    end
+  end
+end

crystal/hamming/src/hamming.cr

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+module Hamming
+  def self.compute(a, b)
+    raise ArgumentError unless a.size == b.size
+    (0..a.size).count {|i| a[i] != b[i]}
+  end
+end
+

crystal/hello-world/src/hello_world.cr

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 # Please implement your solution to hello-world in this file
-puts "Hello, World!"
+class HelloWorld
+  def self.hello
+    "Hello, World!"
+  end
+end
+