Count IP Addresses in Java

The challenge

Implement a function that receives two IPv4 addresses, and returns the number of addresses between them (including the first one, excluding the last one).

All inputs will be valid IPv4 addresses in the form of strings. The last address will always be greater than the first one.

Examples

ips_between("10.0.0.0", "10.0.0.50")  ==   50 
ips_between("10.0.0.0", "10.0.1.0")   ==  256 
ips_between("20.0.0.10", "20.0.1.0")  ==  246

The solution in Java code

Option 1:

public class CountIPAddresses {

  public static long ipsBetween(String start, String end) {
    return convertToLong(end) - convertToLong(start);
  }
  
  private static long convertToLong(String ip) {
    long res = 0;
    for (String s : ip.split("[.]") )
      res = res * 256 + Long.parseLong(s);
    return res;
  }
}

Option 2:

import java.util.Arrays;

public class CountIPAddresses {

    public static long ipsBetween(String start, String end) {
        long[] o = Arrays.stream(start.split("\\.")).mapToLong(Long::parseLong).toArray();
        long[] t = Arrays.stream(end.split("\\.")).mapToLong(Long::parseLong).toArray();

        long diff = 0;
        for (int i = 0; i < 4; i++) {
            diff += (t[i] - o[i]) << (8 * (3-i));
        }
        return diff;
    }
}

Option 3:

public class CountIPAddresses {

  public static long ipsBetween(String start, String end) {
  long result = 0;

        String [] ad1 = start.split("\\.");
        String [] ad2 = end.split("\\.");
        result += (Long.parseLong(ad2[0]) - Long.parseLong(ad1[0]))*256*256*256;
        result += (Long.parseLong(ad2[1]) - Long.parseLong(ad1[1]))*256*256;
        result += (Long.parseLong(ad2[2]) - Long.parseLong(ad1[2]))*256;
        result += (Long.parseLong(ad2[3]) - Long.parseLong(ad1[3]));

        return result;
  }
}

Test cases to validate our solution

import static org.junit.Assert.assertEquals;

import org.junit.Test;

public class CountIPAddressesTest {

	@Test
	public void ipsBetween() throws Exception {
		assertEquals( 50, CountIPAddresses.ipsBetween( "10.0.0.0", "10.0.0.50" ) );
		assertEquals( 246, CountIPAddresses.ipsBetween( "20.0.0.10", "20.0.1.0" ) );
	}

}