tasks a-s

Task/Perfect-numbers/D/perfect-numbers-1.d

@@ -0,0 +1,21 @@
+import std.stdio, std.math, std.range, std.algorithm;
+
+bool isPerfectNumber(in int n) pure nothrow {
+    if (n < 2)
+        return false;
+
+    int sum = 1;
+    foreach (i; 2 .. cast(int)sqrt(cast(real)n) + 1)
+        if (n % i == 0) {
+            immutable int q = n / i;
+            sum += i;
+            if (q > i)
+                sum += q;
+        }
+
+    return sum == n;
+}
+
+void main() {
+    iota(10_000).filter!isPerfectNumber().writeln();
+}

Task/Perfect-numbers/D/perfect-numbers-2.d

@@ -0,0 +1,9 @@
+import std.stdio, std.algorithm, std.range;
+
+bool isPerfect(in int n) /*pure nothrow*/ {
+    return n == iota(1, n - 1).reduce!((s, i) => n % i ? s : s + i)();
+}
+
+void main() {
+    iota(3, 10_000).filter!isPerfect().writeln();
+}