ruby - alphametics

ruby/alphametics/README.md

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+# Alphametics
+
+Write a function to solve alphametics puzzles.
+
+[Alphametics](https://en.wikipedia.org/wiki/Alphametics) is a puzzle where
+letters in words are replaced with numbers.
+
+For example `SEND + MORE = MONEY`:
+
+```text
+  S E N D
+  M O R E +
+-----------
+M O N E Y
+```
+
+Replacing these with valid numbers gives:
+
+```text
+  9 5 6 7
+  1 0 8 5 +
+-----------
+1 0 6 5 2
+```
+
+This is correct because every letter is replaced by a different number and the
+words, translated into numbers, then make a valid sum.
+
+Each letter must represent a different digit, and the leading digit of
+a multi-digit number must not be zero.
+
+Write a function to solve alphametics puzzles.
+
+* * * *
+
+For installation and learning resources, refer to the
+[exercism help page](http://exercism.io/languages/ruby).
+
+For running the tests provided, you will need the Minitest gem. Open a
+terminal window and run the following command to install minitest:
+
+    gem install minitest
+
+If you would like color output, you can `require 'minitest/pride'` in
+the test file, or note the alternative instruction, below, for running
+the test file.
+
+Run the tests from the exercise directory using the following command:
+
+    ruby alphametics_test.rb
+
+To include color from the command line:
+
+    ruby -r minitest/pride alphametics_test.rb
+
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

ruby/alphametics/alphametics.rb

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+# Alphametics class
+class Alphametics
+  def self.solve(puzzle)
+    chars = puzzle.chars & ('A'..'Z').to_a
+    (0..9).to_a.permutation(chars.length).each do |numbers|
+      equation = puzzle.tr(chars.join, numbers.join)
+      next if equation =~ /\b0/
+      return Hash[chars.zip(numbers)] if eval(equation)
+    end
+    {}
+  end
+end

ruby/alphametics/alphametics_test.rb

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+require 'minitest/autorun'
+require_relative 'alphametics'
+
+# Common test data version: 1.2.0 a86a774
+class AlphameticsTest < Minitest::Test
+  def test_puzzle_with_three_letters
+    # skip
+    puzzle = 'I + BB == ILL'
+    expected = { 'B' => 9, 'I' => 1, 'L' => 0 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  def test_solution_must_have_unique_value_for_each_letter
+    # skip
+    puzzle = 'A == B'
+    expected = {}
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  def test_leading_zero_solution_is_invalid
+    # skip
+    puzzle = 'ACA + DD == BD'
+    expected = {}
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  def test_puzzle_with_four_letters
+    # skip
+    puzzle = 'AS + A == MOM'
+    expected = { 'A' => 9, 'M' => 1, 'O' => 0, 'S' => 2 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  def test_puzzle_with_six_letters
+    # skip
+    puzzle = 'NO + NO + TOO == LATE'
+    expected = { 'A' => 0, 'E' => 2, 'L' => 1, 'N' => 7,
+                 'O' => 4, 'T' => 9 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  def test_puzzle_with_seven_letters
+    # skip
+    puzzle = 'HE + SEES + THE == LIGHT'
+    expected = { 'E' => 4, 'G' => 2, 'H' => 5, 'I' => 0,
+                 'L' => 1, 'S' => 9, 'T' => 7 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  # The obvious algorithm can take a long time to solve this puzzle,
+  # but an optimised solution can solve it fairly quickly.
+  # (It's OK to submit your solution without getting this test to pass.)
+  def test_puzzle_with_eight_letters
+    # skip
+    puzzle = 'SEND + MORE == MONEY'
+    expected = { 'D' => 7, 'E' => 5, 'M' => 1, 'N' => 6,
+                 'O' => 0, 'R' => 8, 'S' => 9, 'Y' => 2 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  # The obvious algorithm can take a long time to solve this puzzle,
+  # but an optimised solution can solve it fairly quickly.
+  # (It's OK to submit your solution without getting this test to pass.)
+  def test_puzzle_with_ten_letters
+    # skip
+    puzzle = 'AND + A + STRONG + OFFENSE + AS + A + GOOD == DEFENSE'
+    expected = { 'A' => 5, 'D' => 3, 'E' => 4, 'F' => 7,
+                 'G' => 8, 'N' => 0, 'O' => 2, 'R' => 1,
+                 'S' => 6, 'T' => 9 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+
+  # The obvious algorithm can take a long time to solve this puzzle,
+  # but an optimised solution can solve it fairly quickly.
+  # (It's OK to submit your solution without getting this test to pass.)
+  #
+  # Remove 'do_not_' from the test name to run this test.
+  def do_not_test_puzzle_with_ten_letters_and_199_addends
+    # skip
+    puzzle = 'THIS + A + FIRE + THEREFORE + FOR + ALL + HISTORIES + I + TELL + A + TALE + THAT + FALSIFIES + ITS + TITLE + TIS + A + LIE + THE + TALE + OF + THE + LAST + FIRE + HORSES + LATE + AFTER + THE + FIRST + FATHERS + FORESEE + THE + HORRORS + THE + LAST + FREE + TROLL + TERRIFIES + THE + HORSES + OF + FIRE + THE + TROLL + RESTS + AT + THE + HOLE + OF + LOSSES + IT + IS + THERE + THAT + SHE + STORES + ROLES + OF + LEATHERS + AFTER + SHE + SATISFIES + HER + HATE + OFF + THOSE + FEARS + A + TASTE + RISES + AS + SHE + HEARS + THE + LEAST + FAR + HORSE + THOSE + FAST + HORSES + THAT + FIRST + HEAR + THE + TROLL + FLEE + OFF + TO + THE + FOREST + THE + HORSES + THAT + ALERTS + RAISE + THE + STARES + OF + THE + OTHERS + AS + THE + TROLL + ASSAILS + AT + THE + TOTAL + SHIFT + HER + TEETH + TEAR + HOOF + OFF + TORSO + AS + THE + LAST + HORSE + FORFEITS + ITS + LIFE + THE + FIRST + FATHERS + HEAR + OF + THE + HORRORS + THEIR + FEARS + THAT + THE + FIRES + FOR + THEIR + FEASTS + ARREST + AS + THE + FIRST + FATHERS + RESETTLE + THE + LAST + OF + THE + FIRE + HORSES + THE + LAST + TROLL + HARASSES + THE + FOREST + HEART + FREE + AT + LAST + OF + THE + LAST + TROLL + ALL + OFFER + THEIR + FIRE + HEAT + TO + THE + ASSISTERS + FAR + OFF + THE + TROLL + FASTS + ITS + LIFE + SHORTER + AS + STARS + RISE + THE + HORSES + REST + SAFE + AFTER + ALL + SHARE + HOT + FISH + AS + THEIR + AFFILIATES + TAILOR + A + ROOFS + FOR + THEIR + SAFE == FORTRESSES'
+    expected = { 'A' => 1, 'E' => 0, 'F' => 5, 'H' => 8,
+                 'I' => 7, 'L' => 2, 'O' => 6, 'R' => 3,
+                 'S' => 4, 'T' => 9 }
+    assert_equal expected, Alphametics.solve(puzzle)
+  end
+end