# file: search.py
#
# author: Bob Muller
# date: November 7, 2007
#
# This file contains two search functions, linearSearch and
# binarySearch.
#
# linearSearch looks for an item starting at the front of an arbitrary
# list and working it's way to the back of the list. On average, if the 
# list contains n items, linearSearch will perform n/2 comparisons. 
# When n is 1,000,000,000, for example, linearSearch will perform 
# 500,000,000 comparisons.
#
# binarySearch works only for orderered lists. It starts looking for 
# the item in the middle of the list. If the item isn't found, it will 
# recursively look on either side. binarySearch will perform log_2 n
# comparisons on average. When n is 1,000,000,000, only 30 comparisons
# are required.

def linearSearch(item,lst):

    # print the list for illustration purposes.
    #
    print lst
    if lst == []:
        return False
    else:
        return (item == lst[0] | linearSearch(item,lst[1:]))

def binarySearch(item,lst):

    # print the list for illustration purposes.
    #
    print lst

    if lst == []:
        return False
    else:
        mid = len(lst) / 2
        if item == lst[mid]:
            return True
        else:
            if item > lst[mid]:
                return binarySearch(item, lst[mid+1:])
            else:
                return binarySearch(item, lst[:mid])