func repeatedSubstringPattern(s string) bool {
	n := len(s)
	runes := []rune(s)
	for i := n / 2; 1 <= i; i-- {
		if n%i != 0 {
			continue
		}
		k := i
		for ; k < n && runes[k] == runes[k%i]; k++ {
		}
		if k == n {
			return true
		}
	}
	return false
}