Day 7 Ruby solutions

Author: creideiki

07-1.rb

@@ -0,0 +1,55 @@
+#!/usr/bin/env ruby
+
+class Formula
+  attr_reader :possible, :value
+
+  def initialize(line)
+    val, terms = line.split ':'
+    @value = val.to_i
+    @terms = terms.split.map(&:to_i)
+    @opers = nil
+    @possible = nil
+  end
+
+  def solve_tail(result, partial, opers, terms)
+    return nil if partial > result
+    return opers if result == partial && terms.empty?
+    return nil if terms.empty?
+
+    term = terms[0]
+
+    solution = solve_tail(result, partial + term, opers + [:+], terms[1..])
+    return solution if solution
+
+    solve_tail(result, partial * term, opers + [:*], terms[1..])
+  end
+
+  def solve!
+    @opers = solve_tail(@value, @terms[0], [], @terms[1..])
+    @possible = !@opers.nil?
+  end
+
+  def inspect
+    to_s
+  end
+
+  def to_s
+    s  = "<#{self.class}: #{@value} = "
+    if @opers.nil?
+      s += @terms.to_s
+    else
+      @opers.each_index do |i|
+        s += "#{@terms[i]} #{@opers[i]} "
+      end
+      s += @terms[-1].to_s
+    end
+    s += " #{@possible}" unless @possible.nil?
+    s += '>'
+    s
+  end
+end
+
+lines = File.read('07.input').lines.map(&:strip)
+formulae = lines.map { |l| Formula.new l }
+formulae.map(&:solve!)
+puts formulae.select(&:possible).map(&:value).sum

07-2.rb

@@ -0,0 +1,58 @@
+#!/usr/bin/env ruby
+
+class Formula
+  attr_reader :possible, :value
+
+  def initialize(line)
+    val, terms = line.split ':'
+    @value = val.to_i
+    @terms = terms.split.map(&:to_i)
+    @opers = nil
+    @possible = nil
+  end
+
+  def solve_tail(result, partial, opers, terms)
+    return nil if partial > result
+    return opers if result == partial && terms.empty?
+    return nil if terms.empty?
+
+    term = terms[0]
+
+    solution = solve_tail(result, partial + term, opers + [:+], terms[1..])
+    return solution if solution
+
+    solution = solve_tail(result, partial * term, opers + [:*], terms[1..])
+    return solution if solution
+
+    solve_tail(result, partial * 10.pow(Math.log10(term).floor + 1) + term, opers + [:|], terms[1..])
+  end
+
+  def solve!
+    @opers = solve_tail(@value, @terms[0], [], @terms[1..])
+    @possible = !@opers.nil?
+  end
+
+  def inspect
+    to_s
+  end
+
+  def to_s
+    s  = "<#{self.class}: #{@value} = "
+    if @opers.nil?
+      s += @terms.to_s
+    else
+      @opers.each_index do |i|
+        s += "#{@terms[i]} #{@opers[i]} "
+      end
+      s += @terms[-1].to_s
+    end
+    s += " #{@possible}" unless @possible.nil?
+    s += '>'
+    s
+  end
+end
+
+lines = File.read('07.input').lines.map(&:strip)
+formulae = lines.map { |l| Formula.new l }
+formulae.map(&:solve!)
+puts formulae.select(&:possible).map(&:value).sum