/*
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)
Swift’s built‑in sorted(by:) with a custom comparator
is the idiomatic and efficient way to do this.
*/
import Foundation
/// Returns category rank for sorting.
/// Lower rank = comes earlier.
func category(_ c: Character) -> Int {
if c.isLowercase { return 0 } // lowercase
if c.isUppercase { return 1 } // uppercase
if c.isNumber {
let d = Int(String(c))!
return d % 2 == 1 ? 2 : 3 // odd → 2, even → 3
}
return 4 // fallback (should not happen)
}
/// Custom comparator for sorting characters
func compareChars(_ a: Character, _ b: Character) -> Bool {
let ca = category(a)
let cb = category(b)
if ca != cb {
return ca < cb // sort by category first
}
return a < b // tie-breaker: natural order
}
func sortAlphaNumeric(_ s: String) -> String {
let arr = Array(s)
let sorted = arr.sorted(by: compareChars)
return String(sorted)
}
let s = "a2B3cD8f1Z0"
let result = sortAlphaNumeric(s)
print("Sorted result:", result)
/*
run:
Sorted result: acfBDZ13028
*/
