Java - Regex to check for valid IP's

Regular expressions

A regular expression defines a search pattern for strings. The abbreviation for regular expression is regex. The search pattern can be anything from a simple character, a fixed string or a complex expression containing special characters describing the pattern. The pattern defined by the regex may match one or several times or not at all for a given string.

Regular expressions can be used to search, edit and manipulate text.

Valid IP Address

The basic format of ip addresses format policy is:

• It must start with a number from 0 – 255.
• It must be followed a dot
• This pattern has to repeat for 4 times (eliminating the last dot…)

This is the regex we will use:

"^(([01]?\\d\\d?|2[0-4]\\d|25[0-5])\\.){3}" +

"([01]?\\d\\d?|2[0-4]\\d|25[0-5])$"

This will throw the following output:

• 000.12.12.034 -> valid
  

• 121.234.12.12 -> valid
  

• 23.45.12.56 -> valid
  

• 00.12.123.123123.123 -> invalid
  

• 122.23 -> invalid
  

• Hello.IP -> invalid

Java: Smallest Multiple

This post is made gathering data from other nice sites, but just wanted to have it in a common place.

This is the solution for Project Euler, question #5: Smallest Number.

	public class MyClass {
	public static void main(String args[]) {
	System.out.println(findSmallestMultiple(20));
	}
	/* returns smallest multiple that is evenly divisible by all numbers from 1 - n
	* returns -1 if multiple does not exist
	* works up to n = 20 (long reaches maximum value for values > 20) */
	public static long findSmallestMultiple(int n) {
	for (long i = n; i <= factorial(n); i += n) {
	if (isMultiple(i, n)) {
	return i;
	}
	}
	return -1;
	}
	/* checks every number between 1 and n to see if x is a multiple of every number
	* returns true if x is found to be a multiple of every number, and false if x is
	* found to not be a multiple of any number */
	public static boolean isMultiple(long x, int n) {
	for (int i = 1; i < n; i++) {
	if (x % i != 0) {
	return false;
	}
	}
	return true;
	}
	/* returns the n factorial, or -1 if it does not exist; works up to 20 */
	public static long factorial (long n) {
	if (n > 1) {
	return n * factorial(n - 1);
	}
	else if (n >= 0) {
	return 1;
	}
	else {
	return -1;
	}
	}
	}

view raw SmallestMultiple.java hosted with ❤ by GitHub