Initial data commit

Task/Perfect-shuffle/Java/perfect-shuffle.java

@@ -0,0 +1,33 @@
+import java.util.Arrays;
+import java.util.stream.IntStream;
+
+public class PerfectShuffle {
+
+    public static void main(String[] args) {
+        int[] sizes = {8, 24, 52, 100, 1020, 1024, 10_000};
+        for (int size : sizes)
+            System.out.printf("%5d : %5d%n", size, perfectShuffle(size));
+    }
+
+    static int perfectShuffle(int size) {
+        if (size % 2 != 0)
+            throw new IllegalArgumentException("size must be even");
+
+        int half = size / 2;
+        int[] a = IntStream.range(0, size).toArray();
+        int[] original = a.clone();
+        int[] aa = new int[size];
+
+        for (int count = 1; true; count++) {
+            System.arraycopy(a, 0, aa, 0, size);
+
+            for (int i = 0; i < half; i++) {
+                a[2 * i] = aa[i];
+                a[2 * i + 1] = aa[i + half];
+            }
+
+            if (Arrays.equals(a, original))
+                return count;
+        }
+    }
+}