Solution for Array Addition II on coderbyte - allowing negative numbers.

gistfile1.py

def ArrayAddition(arr): 
    arr = sorted(arr)
    # preprocess array to remove negative numbers
    difference = 0
    for x in arr:
      if x < 0:
        x = abs(x)
        difference = difference + x
    largest = arr.pop() + difference
    while (True):
        result = largest
        for x in reversed(arr):
            result = result - x
            if result == 0:
                return "true"
            elif result < 0:
                # We may end up below 0 because of negative numbers!
                # how do we know when to skip?
                # we don't - so we're going to have to do something more clever
                # how about "preprocessing" the array to shift negative numbers into positive?
                result = result + x
        # If we each the end of the list and haven't returned, pop the largest off
        try:
            arr.pop()
        except:
            return "false"
    
    
# keep this function call here  
# to see how to enter arguments in Python scroll down
print ArrayAddition(raw_input())