Ruby 1.9.2 second attempt
Number of characters: 492 440(426)
Again there is a problem with the non-exact answer. This time this is easily fast enough but for some reason the closest it gets to 824 is 819 instead of 826.
I decided to put this in a new answer since it is using a very different method to my last attempt.
Removing the total of the output (as its not required by spec) is -14 characters.
Fully Obfuscated
def r d,c;d>4?[0]:(k=c.pop;a=[];r(d+1,c).each{|b|a<<[b,k,nil];a<<[nil,k,b]};a)end
def f t,n;[0,2].each{|a|Array===t[a] ?f(t[a],n): t[a]=n.pop}end
def d t;Float===t ?t:d(t[0]).send(t[1],d(t[2]))end
def o c;Float===c ?c.round: "(#{o c[0]}#{c[1]}#{o c[2]})"end
w=a=%w{+ - * /}
4.times{w=w.product a}
*n,l=$<.each(' ').map(&:to_f)
h={}
w.each{|y|r(0,y.flatten).each{|t|f t,n.dup;h[d t]=o t}}
puts h[k=h.keys.min_by{|i|(l-i).abs}]+"=#{k.round}"
Decoded
Coming soon
Test script
#!/usr/bin/env ruby
[
[[50,100,4,2,2,4],203],
[[25,4,9,2,3,10],465],
[[9,8,10,5,9,7],241],
[[3,7,6,2,1,7],824]
].each do |b|
start = Time.now
puts "{[#{b[0]*', '}] #{b[1]}} gives #{`echo "#{b[0]*' '} #{b[1]}" | ruby count-golf.rb`.strip} in #{Time.now-start}"
end
Output
→ ./test.rb
{[50, 100, 4, 2, 2, 4] 203} gives ((4-((2-(2*4))/100))*50)=203 in 1.089726252
{[25, 4, 9, 2, 3, 10] 465} gives ((10*(((3+2)*9)+4))-25)=465 in 1.039455671
{[9, 8, 10, 5, 9, 7] 241} gives (7+(((9/(5/10))+8)*9))=241 in 1.045774539
{[3, 7, 6, 2, 1, 7] 824} gives ((((7-(1/2))*6)*7)*3)=819 in 1.012330419
Details
This constructs the set of ternary trees representing all possible combinations of 5 operators. It then goes through and inserts all permutations of the input numbers into the leaves of these trees. Finally it simply iterates through these possible equations storing them into a hash with the result as index. Then it's easy enough to pick the closest value to the required answer from the hash and display it.
