# Reuse permutations method on my Ruby Q. (#106) Chess960 solution.

def permutations(elements)
return [elements] if elements.size <= 1
result = []
elements.uniq.each do |p|
_elements = elements.dup
_elements.delete_at(elements.index(p))
permutations(_elements).each do |perm|
result << (perm << p)
end
end
result
end

def find(digits, operators, target)
raise “Error: More operators than digits.” if (digits.size <=
operators.size)
operators[digits.size - 2] = nil if (operators.size != digits.size -
1)
found = 0
stars = “*” * 25
perm = permutations(operators)
perm.each do |operator|
expression = digits.zip(operator).flatten.join
value = eval(expression)
if value == target
found += 1
puts stars
puts “#{expression} = #{value}”
puts stars
else
puts “#{expression} = #{value}”
end
end
puts “#{perm.size} possible equations tested.”
puts “#{found} equations satisfied.”
end

if (\$0 == FILE)
digits = ARGV[0] || “123456789”
operators = ARGV[1] || “±-”
target = ARGV[2] || “100”

if (digits =~ /[^1-9]/ || operators =~ /[^-+*/]/)
puts “Usage: #\$0 digits operators target”
exit
end

find(digits.split(//), operators.split(//), target.to_i)
end

for pretty output: change the line which call find method to be:

find(digits.split(//), operators.split(//).map{|e| " #{e} "},
target.to_i)