Code Golf: Countdown Number Game

Answer 1

Python

Number of characters: 548 482 425 421 416 413 408

from operator import *
n=len
def C(N,T):
 R=range(1<

you can call it like this:

>>> print C([50, 100, 4, 2, 2, 4], 203)
((((4+2)*(2+100))/4)+50)

Takes about half a minute on the given examples on an oldish PC.

Here's the commented version:

def countdown(N,T):
  # M is a map: (bitmask of used input numbers -> (expression value -> expression text))                  
  M=[{} for i in range(1<

It works through exhaustive enumeration of all possibilities. It is a bit smart in that if there are two expressions with the same value that use the same input numbers, it discards one of them. It is also smart in how it considers new combinations, using the index into M to prune quickly all the potential combinations that share input numbers.