Data commit

Task/N-queens-problem/Ruby/n-queens-problem-1.rb

@@ -0,0 +1,57 @@
+# 1. Divide n by 12. Remember the remainder (n is 8 for the eight queens
+#    puzzle).
+# 2. Write a list of the even numbers from 2 to n in order.
+# 3. If the remainder is 3 or 9, move 2 to the end of the list.
+# 4. Append the odd numbers from 1 to n in order, but, if the remainder is 8,
+#    switch pairs (i.e. 3, 1, 7, 5, 11, 9, …).
+# 5. If the remainder is 2, switch the places of 1 and 3, then move 5 to the
+#    end of the list.
+# 6. If the remainder is 3 or 9, move 1 and 3 to the end of the list.
+# 7. Place the first-column queen in the row with the first number in the
+#    list, place the second-column queen in the row with the second number in
+#    the list, etc.
+
+
+def n_queens(n)
+  if n == 1
+    return "Q"
+  elsif n < 4
+    puts "no solutions for n=#{n}"
+    return ""
+  end
+
+  evens = (2..n).step(2).to_a
+  odds = (1..n).step(2).to_a
+
+  rem = n % 12  # (1)
+  nums = evens  # (2)
+
+  nums.rotate if rem == 3 or rem == 9  # (3)
+
+  # (4)
+  if rem == 8
+    odds = odds.each_slice(2).flat_map(&:reverse)
+  end
+  nums.concat(odds)
+
+  # (5)
+  if rem == 2
+    nums[nums.index(1)], nums[nums.index(3)] = nums[nums.index(3)], nums[nums.index(1)]
+    nums << nums.delete(5)
+  end
+
+  # (6)
+  if rem == 3 or rem == 9
+    nums << nums.delete(1)
+    nums << nums.delete(3)
+  end
+
+  # (7)
+  nums.map do |q|
+    a = Array.new(n,".")
+    a[q-1] = "Q"
+    a*(" ")
+  end
+end
+
+(1 .. 15).each {|n| puts "n=#{n}"; puts n_queens(n); puts}

Task/N-queens-problem/Ruby/n-queens-problem-2.rb

@@ -0,0 +1,39 @@
+class Queen
+  attr_reader :count
+
+  def initialize(num=8, out=true)
+    @num   = num
+    @out   = out
+    @row   = *0...@num
+    @frame = "+-" + "--" * @num + "+"
+    @count = 0
+    add = Array.new(2 * @num - 1, true)       # \ direction check
+    sub = Array.new(2 * @num - 1, true)       # / direction check
+    solve([], add, sub)
+  end
+
+  private
+  def solve(row, add, sub)
+    y = row.size
+    if y == @num
+      print_out(row) if @out
+      @count += 1
+    else
+      (@row-row).each do |x|
+        next unless add[x+y] and sub[x-y]
+        add[x+y] = sub[x-y] = false
+        solve(row+[x], add, sub)
+        add[x+y] = sub[x-y] = true
+      end
+    end
+  end
+
+  def print_out(row)
+    puts @frame
+    row.each do |i|
+      line = @num.times.map {|j| j==i ? "Q " : ". "}.join
+      puts "| #{line}|"
+    end
+    puts @frame
+  end
+end

Task/N-queens-problem/Ruby/n-queens-problem-3.rb

@@ -0,0 +1,9 @@
+(1..6).each do |n|
+  puzzle = Queen.new(n)
+  puts " #{n} Queen : #{puzzle.count}"
+end
+
+(7..12).each do |n|
+  puzzle = Queen.new(n, false)                # do not display
+  puts " #{n} Queen : #{puzzle.count}"
+end