The second way I’ll implement binary search for Kata Two — Karate Chop will be with recursion. I haven’t used recursion much in my day-to-day work, but I’ve never thought of it as a particularly hard concept to grasp, it just seems that the problems I work aren’t optimally solved with it. The most interesting part of recursion is finding the condition that ends it. Here’s my solutions:

def chopTwo(value, list):
upper = len(list) - 1
lower = 0

return chopTwoRec(upper, lower, value, list)

def chopTwoRec(upper, lower, value, list):
index = (upper + lower) / 2

if index < 0 or upper < lower:
return -1
elif list[index] == value:
return index
elif value > list[index]:
lower = index + 1
elif value < list[index]:
upper = index - 1

return typeTwoRec(upper, lower, value, list)