100-palindrama.md

100 - Palindrama

Written by Michael Zhang, Writeup by Emily Leng

Problem

Given a string stored in args[0], find the longest palindrome inside the string, ignoring the punctuation and spacing during calculations, but including them in the final result.

For example, I did roar again, Niagara! ... or did I? returns I did roar again, Niagara! ... or did I

Notice how the question mark was not part of the palindromic string, so it was not included in the answer (and neither should trailing spaces or new lines).

Hint

Python makes palindrome testing easy (after you remove punctuation, that is) with its ability to reverse strings!

Solution

import string
exclude = set(string.punctuation)
longest = ''
xindex, yindex = 0,0
for x in xrange(0,len(args[0])):
    for y in xrange(0,len(args[0])):
        origStr = args[0][x:y]
        if origStr[0:1] in "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ":
            newStr = ''.join(ch for ch in origStr if ch not in exclude).replace(" ","").lower()
        if newStr == newStr[::-1] and len(newStr) > len(longest):
            longest = newStr
            yindex = y
            xindex = x
print args[0][xindex:yindex].strip(),

Flag

did_you_use_python's_[::-1]_notation?