[QUIZ] Countdown (#7) [Solution]

[email55555 email55555]

Here is my solution.
It is not elegant at all, slow, not OO ... ( I could make it better ... )
Anyway, it does find the solution.

$source = [75,2,8,5,10,10]
$target = 926

$expr = nil
$result = nil
$min_error = nil

def show_solution
puts("source => " + $source * ", ")
puts("target => #$target")
puts("solution => #$expr = #$result")
end

def test(result, expr)
error = ($target - result).abs
if (error == 0)
$expr = expr
$result = result
show_solution
exit # comment out this line if want all solutions
elsif (error < $min_error)
$min_error = error
$expr = expr
$result = result
end
end

def eval_op(op, val1, val2, expr1, expr2, source, source_expr)
result = val1.send(op, val2)
expr = "(#{expr1} #{op} #{expr2})"
test(result, expr)
source << result; source_expr << expr
find(source, source_expr)
source.pop; source_expr.pop
end

def find(source, source_expr)
return if (source.size <= 1)
(0...source.size).each {|i|
(0...source.size).each {|j|
next if (i==j)

if (i < j)
b = source.slice!(j); a = source.slice!(i)
b_expr = source_expr.slice!(j); a_expr = source_expr.slice!(i)
else
a = source.slice!(i); b = source.slice!(j)
a_expr = source_expr.slice!(i); b_expr = source_expr.slice!(j)
end

if (b != 0)
#else skip because a+0==a, a-0==a, a*0==0, a/0 ...

if (i < j) && (a != 0)
#else skip because (1) '+' is commutative (2) 0+b==0
eval_op+, a, b, a_expr, b_expr, source, source_expr)
end

eval_op-, a, b, a_expr, b_expr, source, source_expr)

if (i < j) && (a != 0) && (a != 1) && (b != 1)
#else skip because (1) '*' is commutative (2) 0*b==0 (3) n*1==n
eval_op*, a, b, a_expr, b_expr, source, source_expr)
end

if (a != 0) && (b != 1) # else skip because (1) 0/b==0 (2) n/1==n
eval_op/, a.to_f, b.to_f, a_expr, b_expr, source, source_expr)
end
end

if (i < j)
source[i...i] = a; source[j...j] = b
source_expr[i...i] = a_expr; source_expr[j...j] = b_expr
else
source[j...j] = b; source[i...i] = a
source_expr[j...j] = b_expr; source_expr[i...i] = a_expr
end
}
}
end

$min_error = ($source[0] - $target).abs
$expr = $source[0].to_s
if ($min_error == 0)
show_solution
exit
end

(1...$source.size).each { |i| test($source, $source.to_s) }
find($source.dup, $source.map{|e| e.to_s})
show_solution