KEYS = some random list of numbers
first_index = 0
last_index = 999 (our KEYS is 1000 elements big)
key = the number we're looking for in KEYS

binary_search(KEYS, key, first_index, last_index):
	list_size = (last_index - first_index) + 1
	if list_size == 0
		return KEY_NOT_FOUND
	end

	middle_index = list_size / 2 + first_index

	if key < KEYS[middle_index]
		binary_search(KEYS, key, first_index, middle_index - 1)
	else if key > KEYS[middle_index]
		binary_search(KEYS, key, middle_index + 1, last_index)
	else
		return middle_index
	end