Go: check if string has duplicate symbols

check_string_has_duplicate_symbols.go

func hasDuplicateSymbols(s string) bool {
	seen := make(map[rune]struct{}, len(s))
	for _, r := range s {
		if _, ok := seen[r]; ok {
			return true
		} 
		seen[r] = struct{}{}
	}
	return false
}

// hasDuplicateSymbols("")     -> true
// hasDuplicateSymbols("abc")  -> true
// hasDuplicateSymbols("abca") -> false
// hasDuplicateSymbols(" a ")  -> false