Project Euler > Problem 49 > Prime permutations (Java Solution)

Problem:

The arithmetic sequence, 1487, 4817, 8147, in which each of the terms increases by 3330, is unusual in two ways: (i) each of the three terms are prime, and, (ii) each of the 4-digit numbers are permutations of one another.

There are no arithmetic sequences made up of three 1-, 2-, or 3-digit primes, exhibiting this property, but there is one other 4-digit increasing sequence.

What 12-digit number do you form by concatenating the three terms in this sequence?

Solution:

296962999629

Code:
The solution may include methods that will be found here: Library.java .

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 49
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */

import java.util.Arrays;


public final class p049 implements EulerSolution {
 
 public static void main(String[] args) {
  System.out.println(new p049().run());
 }
 
 
 private static final int LIMIT = 10000;
 
 public String run() {
  boolean[] isPrime = Library.listPrimality(LIMIT - 1);
  for (int base = 1000; base < LIMIT; base++) {
   if (isPrime[base]) {
    for (int step = 1; step < LIMIT; step++) {
     int a = base + step;
     int b = a    + step;
     if (       a < LIMIT && isPrime[a] && hasSameDigits(a, base)
             && b < LIMIT && isPrime[b] && hasSameDigits(b, base)
             && (base != 1487 || a != 4817))
      return "" + base + a + b;
    }
   }
  }
  throw new RuntimeException("Not found");
 }
 
 
 private static boolean hasSameDigits(int x, int y) {
  char[] xdigits = Integer.toString(x).toCharArray();
  char[] ydigits = Integer.toString(y).toCharArray();
  Arrays.sort(xdigits);
  Arrays.sort(ydigits);
  return Arrays.equals(xdigits, ydigits);
 }
 
}