strings.py

# isPalindrome
# Runtime: O(N)
# Space: O(N)

def isPalindrome(strings):
    mid = len(strings)//2
    if len(strings) <= 1:
        return False
    if len(strings) % 2 == 0:
        leftPtr = mid - 1
        rightPtr = mid
    else:
        leftPtr = mid
        rightPtr = mid
    while leftPtr > 0 or rightPtr < len(strings):
        if strings[leftPtr] == strings[rightPtr]:
            leftPtr -= 1
            rightPtr += 1
        else:
            return False
    return True
    
strings = "hilklkhlgyik"
print(isPalindrome(strings))

# caesarCipherEncryptor
# Runtime: O(N)
# Space: O(N)
def caesarCipherEncryptor(string, key):
    # key = key % 26
    newLetters = []
    for letter in string:
        newLetters.append(getNewLetter(letter, key))
    return "".join(newLetters)        
                       
def getNewLetter(letter, key):
    newLetterCode = ord(letter) + key
    if newLetterCode <= 122:
        return chr(newLetterCode)
    else: # to rotate after z makes 122 & above to 1 & adds to 96 to start from 'a'
        return chr(96+ newLetterCode % 122)
    
print(caesarCipherEncryptor("xyz", 2))

def longestPalindromicSubstring(string):
    lis = []
    for i in range(0, len(string)):
        for j in range(i+1, len(string)):
            lis.append(string[i:j])
    for i in lis:
        if len(i) >= 2:
            return isPalindrome(i)
            
def isPalindrome(strings):
    maxString = ""
    flag = True
    mid = len(strings)//2
    if len(strings) % 2 == 0:
        leftPtr = mid - 1
        rightPtr = mid
    else:
        leftPtr = mid
        rightPtr = mid
    while leftPtr > 0 or rightPtr < len(strings):
        if strings[leftPtr] == strings[rightPtr]:
            leftPtr -= 1
            rightPtr += 1
        else:
            flag = False
    if flag == True and len(strings) > len(maxString):
            maxString = strings
            return maxString
    
print(longestPalindromicSubstring("abaxyzzyxf"))