Euler Problem 49 solution

Time (s): ~0.002

package margusmartseppcode.From_40_to_49;

import java.util.Arrays;

public class Problem_49 {

 // Call only if: (n>0&&(i%2==0||i%3==0||i%5==0||i%7==0))
 static boolean isPrimeS(final int n) {
  final int r = (int) Math.floor(Math.sqrt(n));
  for (int f = 5; f <= r; f += 6)
   if (n % f == 0 || n % (f + 2) == 0)
    return false;
  return true;
 }

 static boolean isPerm(char[] a, char[] b) {
  if (a.length != b.length)
   return false;
  Arrays.sort(a);
  Arrays.sort(b);
  return Arrays.equals(a, b);
 }

 static boolean arePerms(int... n) {
  if (n.length == 0)
   return true;
  for (int i = 1; i < n.length; i++)
   if (!isPerm(("" + n[i - 1]).toCharArray(), ("" + n[i])
     .toCharArray()))
    return false;
  return true;
 }

 static boolean arePrimes(int... n) {
  for (int i : n)
   if (!isPrimeS(i))
    return false;

  return true;
 }

 public static void main(String[] args) {
  int a, b, c;
  a = b = c = 0;

  for (a = 1489;; a += 2) {
   if (a % 3 == 0 || a % 5 == 0 || a % 7 == 0)
    continue;
   
   b = a + 3330;
   c = a + 6660;

   if (arePrimes(a, b, c))
    if (arePerms(a, b, c))
     break;
  }
  System.out.println("" + a + b + c);
 }
}

Euler Problem 43 solution

Time (s): ~0.002

package margusmartseppcode.From_40_to_49;

public class Problem_43 {
 static String perms(int n, String s) {
  int fact[] = { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800 };
  return perms(n, s, fact);
 }

 static String perms(int n, String s, int fact[]) {
  StringBuilder sb = new StringBuilder();
  StringBuilder s2 = new StringBuilder(s);

  n--;
  for (int i, g, sl = s2.length(); sl > 0; sl--, n = n % (g)) {
   i = (int) Math.floor(n / (g = fact[sl] / sl));
   sb.append(s2.charAt(i));
   s2.deleteCharAt(i);
  }
  return sb.toString();
 }

 static long cint(String nr) {
  return Long.parseLong(nr);
 }

 static boolean check(String s) {
  return cint(s.substring(1, 4)) % 2 == 0
    && cint(s.substring(2, 5)) % 3 == 0;
 }

 public static void main(String[] args) {
  long sum = 0;
  String p = "";

  for (int i = 1; i < 25; i++)
   sum += (check(p = perms(i, "0134") + "952867") ? cint(p) : 0)
     + (check(p = perms(i, "0146") + "357289") ? cint(p) : 0);


  System.out.println(sum);
 }
}

Euler Problem 24 solution

Time (s): ~0.001

package margusmartseppcode.From_20_to_29;

public class Problem_24 {
 static String perms(int n, String s) {
  int fact[] = { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800 };
  return perms(n, s, fact);
 }

 static String perms(int n, String s, int fact[]) {
  StringBuilder sb = new StringBuilder();
  StringBuilder s2 = new StringBuilder(s);
  n--;
  for (int i, g, sl = s2.length(); sl > 0; sl--, n = n % (g)) {
   i = (int) Math.floor(n / (g = fact[sl] / sl));
   sb.append(s2.charAt(i));
   s2.deleteCharAt(i);
  }
  return sb.toString();
 }

 public static void main(String[] args) {
  System.out.println(perms(1000000, "0123456789"));
 }
}