package main
import (
"fmt"
"sort"
)
/*
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)
Go's sort.Slice() with a custom comparator
is the idiomatic and efficient way to do this.
*/
/// Returns category rank for sorting.
/// Lower rank = comes earlier.
func category(c rune) int {
if c >= 'a' && c <= 'z' {
return 0 // lowercase
}
if c >= 'A' && c <= 'Z' {
return 1 // uppercase
}
if c >= '0' && c <= '9' {
d := int(c - '0')
if d%2 == 1 {
return 2 // odd digits
}
return 3 // even digits
}
return 4 // fallback (should not happen for alphanumeric input)
}
/// Custom comparator for sorting runes
func compare(a, b rune) bool {
ca := category(a)
cb := category(b)
if ca != cb {
return ca < cb // sort by category first
}
return a < b // tie-breaker: natural order
}
func main() {
s := "a2B3cD8f1Z0"
// Convert string to slice of runes
arr := []rune(s)
// Sort using custom comparator
sort.Slice(arr, func(i, j int) bool {
return compare(arr[i], arr[j])
})
// Convert back to string
result := string(arr)
fmt.Println("Sorted result:", result)
}
/*
run:
Sorted result: acfBDZ13028
*/
