"""
We want to sort characters in this strict order:
1. lowercase letters (a–z)
2. uppercase letters (A–Z)
3. odd digits (1,3,5,7,9)
4. even digits (0,2,4,6,8)
Strategy:
---------
Assign each character a "category rank" and sort by:
(category rank, natural character order)
Python's built‑in sorted() with a custom key function
is the idiomatic and efficient way to do this.
"""
def category(c):
"""Return category rank for sorting. Lower rank = earlier."""
if c.islower():
return 0 # lowercase
if c.isupper():
return 1 # uppercase
if c.isdigit():
d = int(c)
return 2 if d % 2 == 1 else 3 # odd → 2, even → 3
return 4 # fallback (should not happen for alphanumeric input)
def sort_alphanumeric(s):
"""
Sort characters using a tuple key:
(category rank, natural character order)
"""
return ''.join(sorted(s, key=lambda ch: (category(ch), ch)))
# Usage
s = "a2B3cD8f1Z0"
result = sort_alphanumeric(s)
print("Sorted result:", result)
"""
run:
Sorted result: acfBDZ13028
"""
