new files

Task/Balanced-ternary/Ruby/balanced-ternary.rb

@@ -0,0 +1,128 @@
+class BalancedTernary
+  def initialize(str = "")
+    if str !~ /^[-+0]+$/
+      raise ArgumentError, "invalid BalancedTernary number: #{str}"
+    end
+    @digits = trim0(str)
+  end
+
+  def self.from_int(value)
+    n = value
+    digits = ""
+    while n != 0
+      quo, rem = n.divmod(3)
+      case rem
+      when 0
+        digits = "0" + digits
+        n = quo
+      when 1
+        digits = "+" + digits
+        n = quo
+      when 2
+        digits = "-" + digits
+        n = quo + 1
+      end
+    end
+    new(digits)
+  end
+
+  def to_int
+    @digits.chars.inject(0) do |sum, char|
+      sum *= 3
+      case char
+      when "+"
+        sum += 1
+      when "-"
+        sum -= 1
+      end
+      sum
+    end
+  end
+  alias :to_i :to_int
+
+  def to_s
+    @digits
+  end
+  alias :inspect :to_s
+
+  ADDITION_TABLE = {
+    "-" => {"-" => ["-","+"], "0" => ["0","-"], "+" => ["0","0"]},
+    "0" => {"-" => ["0","-"], "0" => ["0","0"], "+" => ["0","+"]},
+    "+" => {"-" => ["0","0"], "0" => ["0","+"], "+" => ["+","-"]},
+  }
+
+  def +(other)
+    maxl = [to_s, other.to_s].collect {|s| s.length}.max
+    a = pad0(to_s, maxl)
+    b = pad0(other.to_s, maxl)
+    carry = "0"
+    sum = a.reverse.chars.zip( b.reverse.chars ).inject("") do |sum, (c1, c2)|
+      carry1, digit1 = ADDITION_TABLE[c1][c2]
+      carry2, digit2 = ADDITION_TABLE[carry][digit1]
+      sum = digit2 + sum
+      carry = ADDITION_TABLE[carry1][carry2][1]
+      sum
+    end
+    self.class.new(carry + sum)
+  end
+
+  MULTIPLICATION_TABLE = {
+    "-" => "+0-",
+    "0" => "000",
+    "+" => "-0+",
+  }
+
+  def *(other)
+    product = self.class.new("0")
+    other.to_s.each_char do |bdigit|
+      row = to_s.tr("-0+", MULTIPLICATION_TABLE[bdigit])
+      product += self.class.new(row)
+      product << 1
+    end
+    product >> 1
+  end
+
+  # negation
+  def -@()
+    self * BalancedTernary.new("-")
+  end
+
+  # subtraction
+  def -(other)
+    self + (-other)
+  end
+
+  # shift left
+  def <<(count)
+    @digits = trim0(@digits + "0"*count)
+    self
+  end
+
+  # shift right
+  def >>(count)
+    @digits[-count..-1] = "" if count > 0
+    @digits = trim0(@digits)
+    self
+  end
+
+  private
+
+  def trim0(str)
+    str = str.sub(/^0+/, "")
+    str = "0" if str.empty?
+    str
+  end
+
+  def pad0(str, len)
+    str.rjust(len, "0")
+  end
+end
+
+a = BalancedTernary.new("+-0++0+")
+b = BalancedTernary.from_int(-436)
+c = BalancedTernary.new("+-++-")
+calc = a * (b - c)
+puts "%s\t%d\t%s\n" % ['a', a.to_i, a]
+puts "%s\t%d\t%s\n" % ['b', b.to_i, b]
+puts "%s\t%d\t%s\n" % ['c', c.to_i, c]
+puts "%s\t%d\t%s\n" % ['a*(b-c)', calc.to_i, calc]