The challenge
Take the following IPv4 address: 128.32.10.1
This address has 4 octets where each octet is a single byte (or 8 bits).
- 1st octet
128has the binary representation:10000000 - 2nd octet
32has the binary representation:00100000 - 3rd octet
10has the binary representation:00001010 - 4th octet
1has the binary representation:00000001
So 128.32.10.1 == 10000000.00100000.00001010.00000001
Because the above IP address has 32 bits, we can represent it as the unsigned 32-bit number: 2149583361
Complete the function that takes an unsigned 32-bit number and returns a string representation of its IPv4 address.
Examples
2149583361 ==> "128.32.10.1"
32 ==> "0.0.0.32"
0 ==> "0.0.0.0"
The solution in Java code
Option 1:
public class Solution {
public static String longToIP(long ip) {
return String.format("%d.%d.%d.%d", ip>>>24, (ip>>16)&0xff, (ip>>8)&0xff, ip&0xff);
}
}
Option 2:
public class Solution {
public static String longToIP(final long ip) {
return ((ip >> 24) & 0xFF) + "." +
((ip >> 16) & 0xFF) + "." +
((ip >> 8) & 0xFF) + "." +
(ip & 0xFF);
}
}
Option 3:
public class Solution {
public static String longToIP(long ip) {
StringBuilder sb = new StringBuilder();
long mask = (1<<8)-1;
sb.append(ip>>>24 & mask);
sb.append('.');
sb.append(ip>>>16 & mask);
sb.append('.');
sb.append(ip>>>8 & mask);
sb.append('.');
sb.append(ip & mask);
return sb.toString();
}
}
Test cases to validate our solution
import org.junit.Test;
import java.util.Random;
import static org.junit.Assert.assertEquals;
public class SolutionTest {
@Test
public void sampleTest() {
assertEquals("128.114.17.104", Solution.longToIP(2154959208L));
assertEquals("0.0.0.0", Solution.longToIP(0));
assertEquals("128.32.10.1", Solution.longToIP(2149583361L));
}
private static Random random = new Random();
private static String solution(long ip) {
return (ip >>> 24) % 256 + "." + (ip >>> 16) % 256 + "." + (ip >>> 8) % 256 + "." + ip % 256;
}
@Test
public void randomTest() {
final int Tests = 100;
for (int i = 0; i < Tests; ++i) {
long thirtyBits = random.nextInt(1 << 30);
long twoBits = random.nextInt(1 << 2);
long fullRange = (thirtyBits << 2) | twoBits;
String expected = solution(fullRange);
String actual = Solution.longToIP(fullRange);
assertEquals(expected, actual);
}
}
}