Alphabet

Next in the Alphabet

Challenge Difficulty: Medium | Estimated completion time: ~30 minutes

Create a function which returns the next letters alphabetically in a given string. If the last letter is a “Z”, change the rest of the letters accordingly.

Examples

next_letters("A")
output = "B"
// 'A' becomes 'B' – simple increment.
 
next_letters("ABC")
output = "ABD"
// 'C' becomes 'D' – last character changes without carry.
 
next_letters("Z")
output = "AA"
// 'Z' rolls over to 'A', and since there's no previous letter, we add a new 'A'.
// Think of it like 9 + 1 = 10, here Z + 1 = AA.
 
next_letters("CAZ")
output = "CBA"
// 'Z' → 'A' (carry), 'A' → 'B' (no carry), so "CAZ" becomes "CBA".
// Like incrementing 129 → 130 but in letters.
 
next_letters("")
output = "A"
// Empty input is treated as 0 → return 'A'.

Notes

• Tests will all be in CAPITALS.
• Empty inputs should return a capital “A” (as if it were in letter position 0!).
• Think about the letter “Z” like the number 9 and how it carries over to increment the next letter/digit over.

Solution

Python

def next_letters(text: str) -> str: """Return the next letters alphabetically with carry-over. Args: text: String of uppercase letters Returns: Next alphabetical string (like incrementing a number) """ if not text: return "A" letters = list(text) carry = True for index in range(len(letters) - 1, -1, -1): if not carry: break if letters[index] == "Z": letters[index] = "A" carry = True else: letters[index] = chr(ord(letters[index]) + 1) carry = False if carry: letters.insert(0, "A") return "".join(letters) if __name__ == "__main__": print(next_letters("A")) # B print(next_letters("ABC")) # ABD print(next_letters("Z")) # AA print(next_letters("CAZ")) # CBA print(next_letters("")) # A

Output