def binary_search(list, item):

# low and high keep track of which part of the list you'll search in.

low = 0

high = len(list) - 1

# While you haven't narrowed it down to one element ...

while low <= high:

# ... check the middle element

mid = (low + high) // 2

guess = list[mid]

# Found the item.

if guess == item:

return mid

# The guess was too high.

if guess > item:

high = mid - 1

# The guess was too low.

else:

low = mid + 1

# Item doesn't exist

return None

my_list = [1, 3, 5, 7, 9]

print binary_search(my_list, 3) # => 1

print binary_search(my_list, -1) # => None

This is the code in my book [Grokking Algorithms](https://www.manning.com/bhargava).

- The examples in this book are in Python, but I'd like to get examples in Ruby, Javascript, C, and other languages too. Please add examples in other languages!

- I'm pretty responsive to PRs. That is the quickest way to contribute to this repo.