Character Utilities

01 · Question

Implement two small character helpers:

is_alphanumeric(c): return whether c is an English letter or digit.
to_uppercase(c): convert a lowercase English letter to uppercase; otherwise return c unchanged.

02 · Analysis

ASCII letters and digits occupy contiguous ranges, so both helpers use direct range checks:

Alphanumeric means a-z, A-Z, or 0-9.
Uppercase conversion keeps the character's offset from 'a' and applies it from 'A'.

The point: reason with character ranges and relative offsets instead of memorizing numeric ASCII codes.

Complexity: both helpers run in $O(1)$ time and use $O(1)$ space.

03 · Solution

Two focused implementations

1def is_alphanumeric(c: str) -> bool:
2    return ('a' <= c <= 'z') or \
3           ('A' <= c <= 'Z') or \
4           ('0' <= c <= '9')

1def to_uppercase(c: str) -> str:
2    if not ('a' <= c <= 'z'):
3        return c
4    return chr(ord(c) - ord('a') + ord('A'))