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Problem41.java
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Problem41.java
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/*
* Prompt: What is the largest n-digit pandigital prime that exists?
*
* Execute: javac Problem41.java; java Problem41; rm Problem41.class
*
* Answer: 7652413
*/
import java.util.Arrays;
public class Problem41 {
private static final char[] pandigital = {'1', '2', '3', '4', '5', '6', '7', '8', '9'};
public static void main(String[] args) {
int limit = 9999999; // Arbitrary
boolean[] primes = sieve(limit);
int largePandigitalPrime = 0;
for (int i = 0; i < limit; i++)
if (primes[i] && isPandigital(i))
largePandigitalPrime = i;
System.out.println(largePandigitalPrime);
}
private static boolean[] sieve(int n) {
boolean primes[] = new boolean[n];
Arrays.fill(primes, true);
for (int p = 2; p * p < n; p++)
if (primes[p])
for (int i = p * 2; i < n; i += p)
primes[i] = false;
return primes;
}
private static boolean isPandigital(int n) {
char[] c = Integer.toString(n).toCharArray();
Arrays.sort(c);
for (int i = 0; i < c.length; i++)
if (c[i] != pandigital[i])
return false;
return true;
}
}