Data commit

Task/M-bius-function/D/m-bius-function.d

@@ -0,0 +1,56 @@
+import std.math;
+import std.stdio;
+
+immutable MU_MAX = 1_000_000;
+
+int mobiusFunction(int n) {
+    static initialized = false;
+    static int[MU_MAX + 1] MU;
+
+    if (initialized) {
+        return MU[n];
+    }
+
+    // populate array
+    MU[] = 1;
+    int root = cast(int) sqrt(cast(real) MU_MAX);
+
+    for (int i = 2; i <= root; i++) {
+        if (MU[i] == 1) {
+            // for each factor found, swap + and -
+            for (int j = i; j <= MU_MAX; j += i) {
+                MU[j] *= -i;
+            }
+            // square factor = 0
+            for (int j = i * i; j <= MU_MAX; j += i * i) {
+                MU[j] = 0;
+            }
+        }
+    }
+
+    for (int i = 2; i <= MU_MAX; i++) {
+        if (MU[i] == i) {
+            MU[i] = 1;
+        } else if (MU[i] == -i) {
+            MU[i] = -1;
+        } else if (MU[i] < 0) {
+            MU[i] = 1;
+        } else if (MU[i] > 0) {
+            MU[i] = -1;
+        }
+    }
+
+    initialized = true;
+    return MU[n];
+}
+
+void main() {
+    writeln("First 199 terms of the möbius function are as follows:");
+    write("    ");
+    for (int n = 1; n < 200; n++) {
+        writef("%2d  ", mobiusFunction(n));
+        if ((n + 1) % 20 == 0) {
+            writeln;
+        }
+    }
+}