Question

3. Did you ever wonder what are the longest words that when spelled backwards form other valid words? Well, now you get to answer that question (even if you never asked it ;-)). Write a function writeLongestBackwardsWordsToFile(M) that writes a file ‘topMBackwardsWords.txt’ (e.g. ‘top3BackwardsWords.txt’ if M = 3), containing the M longest words and their corresponding backwards word together on one line, and different word pairs on different lines. Try not to duplicate the same word pair (with order reversed) on a different line, but if you cannot solve the problem without doing this no points will be deducted. See the following expected output for ‘top3BackwardsWords.txt’:

Hint: Break the function into 3 sections: 1) read in wordlist.txt and convert to a set, 2) for-loop through the set of words and check if the reverse word is also in the set (sets are very fast at checking membership, lists are slowww…), forming a list of reversible words. 3) Sort the list of words by length (make a list of tuples) and write first M to file.

Answer 1

# python code

def writeLongestBackwardsWordsToFile(M):
    # read in wordlist.txt and convert to a set
    readWords = open('wordlist.txt')
    wordSet = set(readWords.read().split())
    readWords.close()
    wordList = []
    outFIle = "top%dBackwardsWords.txt" % (M)

    # for-loop through the set of words and check if the reverse word is also in the set
    for i in wordSet.copy():
        if i[::-1] in wordSet:
            wordList.append(i)
            wordSet.remove(i)
    # Sort the list of words by length
    wordList.sort(key=len, reverse=True)

    # write first M to file.
    file = open(outFIle, "w")
    for x in range(0, M):
        file.write(wordList[x])
        file.write("\t")
        file.write(wordList[x][::-1])
        file.write("\n")
    file.close()

writeLongestBackwardsWordsToFile(3)

'''
top3BackwardsWords.txt

redrawer    rewarder
halalah halalah
reifier reifier

'''

Answer 2

# python code

def writeLongestBackwardsWordsToFile(M):
    # read in wordlist.txt and convert to a set
    readWords = open('wordlist.txt')
    wordSet = set(readWords.read().split())
    readWords.close()
    wordList = []
    outFIle = "top%dBackwardsWords.txt" % (M)

    # for-loop through the set of words and check if the reverse word is also in the set
    for i in wordSet.copy():
        if i[::-1] in wordSet:
            wordList.append(i)
            wordSet.remove(i)
    # Sort the list of words by length
    wordList.sort(key=len, reverse=True)

    # write first M to file.
    file = open(outFIle, "w")
    for x in range(0, M):
        file.write(wordList[x])
        file.write("\t")
        file.write(wordList[x][::-1])
        file.write("\n")
    file.close()

writeLongestBackwardsWordsToFile(3)

'''
top3BackwardsWords.txt

redrawer    rewarder
halalah halalah
reifier reifier

'''

Answer 3

# python code

def writeLongestBackwardsWordsToFile(M):
    # read in wordlist.txt and convert to a set
    readWords = open('wordlist.txt')
    wordSet = set(readWords.read().split())
    readWords.close()
    wordList = []
    outFIle = "top%dBackwardsWords.txt" % (M)

    # for-loop through the set of words and check if the reverse word is also in the set
    for i in wordSet.copy():
        if i[::-1] in wordSet:
            wordList.append(i)
            wordSet.remove(i)
    # Sort the list of words by length
    wordList.sort(key=len, reverse=True)

    # write first M to file.
    file = open(outFIle, "w")
    for x in range(0, M):
        file.write(wordList[x])
        file.write("\t")
        file.write(wordList[x][::-1])
        file.write("\n")
    file.close()

writeLongestBackwardsWordsToFile(3)

'''
top3BackwardsWords.txt

redrawer    rewarder
halalah halalah
reifier reifier

'''