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A palindrome is a word, phrase, number, or other sequence of characters which reads the same backward as forward, such as madam or racecar. Sentence-length palindromes may be written when allowances are made for adjustments to capital letters, punctuation, and word dividers, such as "A man, a plan, a canal, Panama!", "Was it a car or a cat I saw?" or "No 'x' in Nixon". Write a function that takes a string as an argument and returns True if the string is a palindrome and False otherwise.

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Answer:

The solution code is written in Python 3.

  1. import math
  3. def processString(myStr):
  4.    process = myStr.lower()
  5.    process = process.replace(" ","")
  6.    
  7.    p_list = '''!()-[]{};:'"\,<>./?@#$%^&*_~'''
  8.    for p in p_list:
  9.        process = process.replace(p, "")
  10.    
  11.    return process
  13. def isPalindrome(myStr):
  14.    myStr = processString(myStr)
  15.    for i in range(0, math.ceil(len(myStr))):
  16.        lastIndex = len(myStr) - 1 - i
  17.        if(myStr[0] != myStr[lastIndex]):
  18.            return False  
  19.        
  20.        return True  
  22. print(isPalindrome("racecar"))
  23. print(isPalindrome("apple"))
  24. print(isPalindrome("Was it a car or a cat I saw?"))
  25. print(isPalindrome("No 'x' in Nixon"))
  26. print(isPalindrome("Programming is fun!"))

Explanation:

Since the palindrome function is expected to work on a sentence, we need to process the string prior to checking if the string is a palindrome. To process a string, a separate function is written, processString() with one parameter, "myStr" that will accept one input string. (Line 3 - 11)

Within the processString() function, there are three processing steps on the input string, my_str:

  1. convert all letters in string to lowercase using Python string lower() method (Line 4)
  2. remove all word dividers (Line 5) using replace() method
  3. remove all punctuation (Line 7-9). To remove punctuation, we need to define a punctuation list (Line 7). Next, use for-loop to traverse the punctuation list and whenever there is a punctuation appears in the input string, remove it using replace() method (Line 8-9).

After the function processString() is ready, we can proceed to work on the palindrome function, isPalindrome(). This function has one parameter that will accept one input string.

Within the function isPalindrome(), we call the function processString by passing the input string, my_str as argument (Line 14). The function processString() will operate on the my_str by converting all the letters to lowercase, removing all the word dividers and punctuation.

Next the processed string will be returned to my_str. Next, within a for-loop, traverse through the letters in my_str and compare the first letter with the last letter, second letter with second last letter until it reaches the middle point. (Line 15-17) If any comparison is found unmatched, return false since it is not a palindrome. If there is no unmatched found in the for-loop, the function will just return true.

At last, we test our function isPalindrome() with several test strings (Line 22 26) and the output is as follows:

True

False

True

True

False

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