subpalindrome.py

# radar==radar
#

# --------------
# User Instructions
#
# Write a function, longest_subpalindrome_slice(text) that takes 
# a string as input and returns the i and j indices that 
# correspond to the beginning and end indices of the longest 
# palindrome in the string. 
#
# Grading Notes:
# 
# You will only be marked correct if your function runs 
# efficiently enough. We will be measuring efficency by counting
# the number of times you access each string. That count must be
# below a certain threshold to be marked correct.
#
# Please do not use regular expressions to solve this quiz!

def longest_subpalindrome_slice(text):
    "Return (i, j) such that text[i:j] is the longest palindrome in text."
    if text=='':return (0,0)
    palindromes = [grow(text, start, end)
                   for start in range(len(text))
                   for end in (start, start+1) ]
    print (palindromes)
    return max(palindromes, key=length)

def length(slice):
    a,b=slice
    return b-a

def grow(text, start, end):
    while (start >0 and end < len(text)
           and text[start-1].upper() == text[end].upper() ):
        start -=1; end +=1
    return (start,end)
    
def test():
    L = longest_subpalindrome_slice
    assert L('racecar') == (0, 7)
    assert L('Racecar') == (0, 7)
    assert L('RacecarX') == (0, 7)
    assert L('Race carr') == (7, 9)
    assert L('') == (0, 0)
    assert L('something rac e car going') == (8,21)
    assert L('xxxxx') == (0, 5)
    assert L('Mad am I ma dam.') == (0, 15)
    return 'tests pass'

print (test())