Data commit

Task/Perfect-shuffle/D/perfect-shuffle.d

@@ -0,0 +1,31 @@
+import std.stdio;
+
+void main() {
+    auto sizes = [8, 24, 52, 100, 1020, 1024, 10_000];
+    foreach(s; sizes) {
+        writefln("%5s : %5s", s, perfectShuffle(s));
+    }
+}
+
+int perfectShuffle(int size) {
+    import std.exception : enforce;
+    enforce(size%2==0);
+
+    import std.algorithm : copy, equal;
+    import std.range;
+    int[] orig = iota(0, size).array;
+
+    int[] process;
+    process.length = size;
+    copy(orig, process);
+
+    for(int count=1; true; count++) {
+        process = roundRobin(process[0..$/2], process[$/2..$]).array;
+
+        if (equal(orig, process)) {
+            return count;
+        }
+    }
+
+    assert(false, "How did this get here?");
+}