Initial data commit

Task/Successive-prime-differences/Java/successive-prime-differences.java

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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class SuccessivePrimeDifferences {
+    private static Integer[] sieve(int limit) {
+        List<Integer> primes = new ArrayList<>();
+        primes.add(2);
+        boolean[] c = new boolean[limit + 1];// composite = true
+        // no need to process even numbers > 2
+        int p = 3;
+        while (true) {
+            int p2 = p * p;
+            if (p2 > limit) {
+                break;
+            }
+            for (int i = p2; i <= limit; i += 2 * p) {
+                c[i] = true;
+            }
+            do {
+                p += 2;
+            } while (c[p]);
+        }
+        for (int i = 3; i <= limit; i += 2) {
+            if (!c[i]) {
+                primes.add(i);
+            }
+        }
+
+        return primes.toArray(new Integer[0]);
+    }
+
+    private static List<List<Integer>> successivePrimes(Integer[] primes, Integer[] diffs) {
+        List<List<Integer>> results = new ArrayList<>();
+        int dl = diffs.length;
+        outer:
+        for (int i = 0; i < primes.length - dl; i++) {
+            Integer[] group = new Integer[dl + 1];
+            group[0] = primes[i];
+            for (int j = i; j < i + dl; ++j) {
+                if (primes[j + 1] - primes[j] != diffs[j - i]) {
+                    continue outer;
+                }
+                group[j - i + 1] = primes[j + 1];
+            }
+            results.add(Arrays.asList(group));
+        }
+        return results;
+    }
+
+    public static void main(String[] args) {
+        Integer[] primes = sieve(999999);
+        Integer[][] diffsList = {{2}, {1}, {2, 2}, {2, 4}, {4, 2}, {6, 4, 2}};
+        System.out.println("For primes less than 1,000,000:-\n");
+        for (Integer[] diffs : diffsList) {
+            System.out.printf("  For differences of %s ->\n", Arrays.toString(diffs));
+            List<List<Integer>> sp = successivePrimes(primes, diffs);
+            if (sp.isEmpty()) {
+                System.out.println("    No groups found");
+                continue;
+            }
+            System.out.printf("    First group   = %s\n", Arrays.toString(sp.get(0).toArray(new Integer[0])));
+            System.out.printf("    Last group    = %s\n", Arrays.toString(sp.get(sp.size() - 1).toArray(new Integer[0])));
+            System.out.printf("    Number found  = %d\n", sp.size());
+            System.out.println();
+        }
+    }
+}