package main

func isValidPart(part string) bool {
	switch len(part) {
	case 1: // \d
		return true
	case 2: // [^0]\d
		return part[0] != '0'
	case 3: // 1\d{2} || 2[0-4]\d || 25[1-5]
		if part[0] != '2' {
			return part[0] == '1'
		}
		return part[1] <= '4' ||
			(part[1] == '5' && part[2] <= '5')
	}
	return false
}

func restoreIpAddresses(s string) []string {
	result := []string{}
	strLen := len(s)
	if strLen < 4 || 12 < strLen {
		return result
	}
	for i := 1; i < 4 && i < strLen-2; i++ {
		for j := i + 1; j < i+4 && j < strLen-1; j++ {
			for k := j + 1; k < j+4 && k < strLen; k++ {
				if isValidPart(s[0:i]) && isValidPart(s[i:j]) &&
					isValidPart(s[j:k]) && isValidPart(s[k:]) {
					result = append(result, s[0:i]+"."+s[i:j]+"."+s[j:k]+"."+s[k:])
				}
			}
		}
	}
	return result
}

// func main() {
// 	fmt.Println(restoreIpAddresses("25525511135"))
// 	fmt.Println(restoreIpAddresses("0000"))
// 	fmt.Println(restoreIpAddresses("00000"))
// }