Make 10, 四則パズル

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与えられた数を順不同に用い、四則を自由な順に適用して10を作るパズル

make10.rb

ANS=10.0

def dfs(a)
  if a.size == 1
    puts a[0][:exp] if a[0][:val] == ANS
    return
  end
  (0...a.size).each {|i|
    ((i+1)...a.size).each {|j|
      rest = []
      (0...a.size).each {|idx|
        rest << a[idx] if idx!=i && idx!=j
      }
      x = a[i]
      y = a[j]
      dfs [ { :val => x[:val] + y[:val], :exp => "(+ #{x[:exp]} #{y[:exp]})" } ] + rest
      dfs [ { :val => x[:val] * y[:val], :exp => "(* #{x[:exp]} #{y[:exp]})" } ] + rest
      dfs [ { :val => x[:val] - y[:val], :exp => "(- #{x[:exp]} #{y[:exp]})" } ] + rest
      dfs [ { :val => y[:val] - x[:val], :exp => "(- #{y[:exp]} #{x[:exp]})" } ] + rest
      dfs [ { :val => x[:val] / y[:val], :exp => "(/ #{x[:exp]} #{y[:exp]})" } ] + rest
      dfs [ { :val => y[:val] / x[:val], :exp => "(/ #{y[:exp]} #{x[:exp]})" } ] + rest
    }
  }
end

def solve(ls)
  dfs ls.map {|x| { :val => x.to_f, :exp => x.to_s } }
end

solve [1,1,5,8]