Data commit

Task/Sudoku/Ruby/sudoku.rb

@@ -0,0 +1,91 @@
+def read_matrix(data)
+  lines = data.lines
+  9.times.collect { |i| 9.times.collect { |j| lines[i][j].to_i } }
+end
+
+def permissible(matrix, i, j)
+  ok = [nil, *1..9]
+  check = ->(x,y) { ok[matrix[x][y]] = nil  if matrix[x][y].nonzero? }
+  # Same as another in the column isn't permissible...
+  9.times { |x| check[x, j] }
+  # Same as another in the row isn't permissible...
+  9.times { |y| check[i, y] }
+  # Same as another in the 3x3 block isn't permissible...
+  xary = [ *(x = (i / 3) * 3) .. x + 2 ]        #=> [0,1,2], [3,4,5] or [6,7,8]
+  yary = [ *(y = (j / 3) * 3) .. y + 2 ]
+  xary.product(yary).each { |x, y| check[x, y] }
+  # Gathering only permitted one
+  ok.compact
+end
+
+def deep_copy_sudoku(matrix)
+  matrix.collect { |row| row.dup }
+end
+
+def solve_sudoku(matrix)
+  loop do
+    options = []
+    9.times do |i|
+      9.times do |j|
+        next if matrix[i][j].nonzero?
+        p = permissible(matrix, i, j)
+        # If nothing is permissible, there is no solution at this level.
+        return if p.empty?              # return nil
+        options << [i, j, p]
+      end
+    end
+    # If the matrix is complete, we have a solution...
+    return matrix if options.empty?
+
+    i, j, permissible = options.min_by { |x| x.last.length }
+
+    # If there is an option with only one solution, set it and re-check permissibility
+    if permissible.length == 1
+      matrix[i][j] = permissible[0]
+      next
+    end
+
+    # We have two or more choices. We need to search both...
+    permissible.each do |v|
+      mtmp = deep_copy_sudoku(matrix)
+      mtmp[i][j] = v
+      ret = solve_sudoku(mtmp)
+      return ret if ret
+    end
+
+    # We did an exhaustive search on this branch and nothing worked out.
+    return
+  end
+end
+
+def print_matrix(matrix)
+  puts "Impossible" or return  unless matrix
+
+  border = "+-----+-----+-----+"
+  9.times do |i|
+    puts border if i%3 == 0
+    9.times do |j|
+      print j%3 == 0 ? "|" : " "
+      print matrix[i][j] == 0 ? "." : matrix[i][j]
+    end
+    puts "|"
+  end
+  puts border
+end
+
+data = <<EOS
+394__267_
+___3__4__
+5__69__2_
+_45___9__
+6_______7
+__7___58_
+_1__67__8
+__9__8___
+_264__735
+EOS
+
+matrix = read_matrix(data)
+print_matrix(matrix)
+puts
+print_matrix(solve_sudoku(matrix))