A-M baby

Task/Hofstadter-Q-sequence/D/hofstadter-q-sequence-1.d

@@ -0,0 +1,17 @@
+import std.stdio, std.algorithm, std.functional, std.range;
+
+int Q(int n) {
+    assert(n > 0);
+    alias memoize!Q mQ;
+    if (n == 1 || n == 2)
+        return 1;
+    else
+        return mQ(n - mQ(n - 1)) + mQ(n - mQ(n - 2));
+}
+
+void main() {
+    writeln("Q(n) for n = [1..10] is: ", map!Q(iota(1, 11)));
+    writeln("Q(1000) = ", Q(1000));
+    writefln("Q(i) is less than Q(i-1) for i [2..100_000] %d times.",
+             count!(i => Q(i) < Q(i-1))(iota(2, 100_001)));
+}

Task/Hofstadter-Q-sequence/D/hofstadter-q-sequence-2.d

@@ -0,0 +1,23 @@
+import std.stdio, std.algorithm, std.range, std.array;
+
+struct Q {
+    static Appender!(uint[]) s;
+
+    /*nothrow*/ static this() {
+        s ~= [0, 1, 1];
+    }
+
+    static uint opCall(in int n) /*nothrow*/ {
+        assert(n > 0);
+        foreach (immutable i; s.data.length .. n + 1)
+            s ~= s.data[i - s.data[i - 1]] + s.data[i - s.data[i - 2]];
+        return s.data[n];
+    }
+}
+
+void main() {
+    writeln("Q(n) for n = [1..10] is: ", map!Q(iota(1, 11)));
+    writeln("Q(1000) = ", Q(1000));
+    writefln("Q(i) is less than Q(i-1) for i [2..100_000] %d times.",
+             count!(i => Q(i) < Q(i-1))(iota(2, 100_001)));
+}