# reads in a list of words, binary search for user-supplied word
# assumes sorted list
# ECS 10, May 22, 2009
# Matt Bishop
import string

# search a list of words for a word (binary search)
# parameters: word, the word to find in the list
#             wordlist, the list of words
#             low, low bound of search in wordlist
#             high, high bound of search in wordlist
# returns: index (+1) of word in list
#          -1 if not in list
def search(word, wordlist, low, high):
        # if low ever passes high, the word isn't in the list
        if low > high:
                return -1
        
        # check the middle word
        mid = (low + high) / 2
        if word == wordlist[mid]:
                # match -- we're done!
                return mid + 1
        elif word < wordlist[mid]:
                # word comes before middle word
                # reduce the high index of the interval
                return search(word, wordlist, low, mid-1)
        else:
                # word comes after middle word
                # advance the low index of the interval
                return search(word, wordlist, mid+1, high)
                

# append words from a file to a list; assumes one word per line
# note: lines separated by *newlines*, not *carriage returns*
# parameters: wordlist, list to append words to
# returns: True if words loaded successfully
#          False if problem opening file
def loadfile(wordlist):
        # open the file, trapping errors
        try:
                infile = open("list.txt", "r")
        except IOError, errmsg:
                # say why it failed, return error code
                print "Could not open 'xxx.txt':", errmsg
                return False
        # go through the file line by line
        for i in infile:
                # strip any trailing white space (inc. newline)
                i = string.rstrip(i)
                # tack the word onto the list
                wordlist.append(i)
        # all done! close file and return success code
        infile.close()
        return True


# this puts it all together
def main():
        # initialize word list
        wordlist = []
        # load the word list; on error, quit
        if not loadfile(wordlist):
                return
        # loop 
        while True:
                # read in word; quit on EOF
                try:
                        find = raw_input("What word should I look for EOF to quit)? ")
                except EOFError:
                        return
                # find the word if it's there
                found = search(find, wordlist, 0, len(wordlist)-1)
                # announce result
                if found == -1:
                        print "'%s' is not in the list" % find
                else:
                        print "'%s' is word number %d" % (find, found)

main()