UVa 524 Prime Ring Problem Solution in Java

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.StringTokenizer;

/**
 * Created by dhruv.pancholi on 20/11/16.
 */
public class Main {

    private static boolean[] onStack = new boolean[16];

    private static void dfs(List<Integer>[] adjacency, String out, int node, int n, int N) {
        if (n == 1) {
            if (adjacency[node - 1].get(0) == 1) System.out.println(out);
            return;
        }
        for (Integer i : adjacency[node - 1]) {
            if (onStack[i - 1] || i > N) {
                continue;
            } else {
                out += " " + i;
                onStack[i - 1] = true;
                dfs(adjacency, out, i, n - 1, N);
                out = out.substring(0, out.lastIndexOf(" "));
                onStack[i - 1] = false;
            }
        }
    }

    public static void main(String[] args) throws FileNotFoundException {
        InputReader in = new InputReader(System.in);
        SieveOfEratosthenes soe = new SieveOfEratosthenes(50);
        List<Integer>[] adjacency;
        adjacency = new List[16];
        for (int i = 0; i < 16; i++) {
            adjacency[i] = new ArrayList<Integer>();
        }
        for (int i = 0; i < 16; i++) {
            for (int j = i + 1; j < 16; j++) {
                if (soe.isPrime(i + j + 2)) {
                    adjacency[i].add(j + 1);
                    adjacency[j].add(i + 1);
                }
            }
        }

        int c = 0;
        while (true) {
            LinkedList<Integer> stack = new LinkedList<Integer>();
            stack.add(1);
            onStack[0] = true;
            int n = in.nextInt();
            if (c != 0) System.out.println();
            System.out.println("Case " + (++c) + ":");
            if (n == 1) {
                System.out.println(1);
            } else {
                dfs(adjacency, "1", 1, n, n);
            }
        }
    }

    private static class SieveOfEratosthenes {
        private boolean[] a;

        public SieveOfEratosthenes(int N) {
            a = new boolean[N + 1];
            for (int i = 0; i <= N; i++) {
                a[i] = true;
            }
            a[0] = false;
            a[1] = false;

            int root = (int) Math.sqrt(N);
            for (int i = 2; i <= root; i++) {
                for (int j = 2 * i; j <= N; j += i) {
                    a[j] = false;
                }
            }
        }

        public boolean[] getArray() {
            return a;
        }

        public boolean isPrime(int n) {
            return a[n];
        }

        public List<Integer> getPrimes() {
            List<Integer> list = new ArrayList<Integer>();
            for (int i = 1; i < a.length; i++) {
                if (a[i]) {
                    list.add(i);
                }
            }
            return list;
        }
    }

    private static class InputReader {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream));
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (Exception e) {
                    System.exit(0);
                }
            }
            return tokenizer.nextToken();
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
    }
}

Sample Input:

6
8

Sample Output:

Case 1:
1 4 3 2 5 6
1 6 5 2 3 4

Case 2:
1 2 3 8 5 6 7 4
1 2 5 8 3 4 7 6
1 4 7 6 5 8 3 2
1 6 7 4 3 8 5 2