###
# binary_search.py
#
# author: Kristina Striegnitz
#
# version: 2/7/2010
#
# Check whether a given element is in a list. List must be ordered.
###


def binary_search (value, l):

    low_index = 0
    high_index = len(l) - 1

    while low_index <= high_index:

        mid_index = (low_index + high_index) / 2
        mid_val = l[mid_index]

        if mid_val == value:
            return True

        elif mid_val < value:
            low_index = mid_index + 1

        else:
            high_index = mid_index - 1

    return False

    
def binary_search2(value, l):

    while l != []:

        mid_index = len(l) / 2
        mid_val = l[mid_index]

        if mid_val == value:
            return True

        elif mid_val < value:
            l = l[mid_index+1: ] # everything from the middle to the end

        else:
            l = l[ :mid_index] # everything from the beginning to the middle

    return False