Just another update

Task/Sierpinski-triangle/D/sierpinski-triangle-1.d

@@ -1,6 +1,6 @@
-import std.stdio, std.algorithm, std.string, std.array;
+void main() /*@safe*/ {
+    import std.stdio, std.algorithm, std.string, std.array;
 
-void main() {
     enum level = 4;
     auto d = ["*"];
     foreach (immutable n; 0 .. level) {
@@ -8,5 +8,5 @@ void main() {
         d = d.map!(a => sp ~ a ~ sp).array ~
             d.map!(a => a ~ " " ~ a).array;
     }
-    d.join("\n").writeln;
+    d.join('\n').writeln;
 }

Task/Sierpinski-triangle/D/sierpinski-triangle-2.d

@@ -1,19 +1,14 @@
-import std.string;
+import std.string, std.range, std.algorithm;
 
-string sierpinski(int n) {
-    auto parts = ["*"];
-    auto space = " ";
-    foreach (i; 0 .. n) {
-        string[] parts2;
-        foreach (x; parts)
-            parts2 ~= space ~ x ~ space;
-        foreach (x; parts)
-            parts2 ~= x ~ " " ~ x;
-        parts = parts2;
-        space ~= space;
+string sierpinski(int level) pure nothrow /*@safe*/ {
+    auto d = ["*"];
+    foreach (immutable i; 0 .. level) {
+        immutable sp = " ".replicate(2 ^^ i);
+        d = d.map!(a => sp ~ a ~ sp).array ~
+            d.map!(a => a ~ " " ~ a).array;
     }
-    return parts.join("\n");
+    return d.join('\n');
 }
 
-pragma(msg, sierpinski(4));
+pragma(msg, 4.sierpinski);
 void main() {}

Task/Sierpinski-triangle/D/sierpinski-triangle-3.d

@@ -0,0 +1,17 @@
+void showSierpinskiTriangle(in uint order) nothrow @safe @nogc {
+    import core.stdc.stdio: putchar;
+
+    foreach_reverse (immutable y; 0 .. 2 ^^ order) {
+        foreach (immutable _; 0 .. y)
+            ' '.putchar;
+        foreach (immutable x; 0 .. 2 ^^ order - y) {
+            putchar((x & y) ? ' ' : '*');
+            ' '.putchar;
+        }
+        '\n'.putchar;
+    }
+}
+
+void main() nothrow @safe @nogc {
+    4.showSierpinskiTriangle;
+}

Task/Sierpinski-triangle/D/sierpinski-triangle-4.d

@@ -0,0 +1,42 @@
+import core.stdc.stdio: putchar;
+import std.algorithm: swap;
+
+
+void showSierpinskiTriangle(in uint nLevels) nothrow @safe
+in {
+    assert(nLevels > 0);
+} body {
+    alias Row = bool[];
+
+    static void applyRules(in Row r1, Row r2) pure nothrow @safe @nogc {
+        r2[0] = r1[0] || r1[1];
+        r2[$ - 1] = r1[$ - 2] || r1[$ - 1];
+        foreach (immutable i; 1 .. r2.length - 1)
+            r2[i] = r1[i - 1] != r1[i] || r1[i] != r1[i + 1];
+    }
+
+    static void showRow(in Row r) nothrow @safe @nogc {
+        foreach (immutable b; r)
+            putchar(b ? '#' : ' ');
+        '\n'.putchar;
+    }
+
+    immutable width = 2 ^^ (nLevels + 1) - 1;
+    auto row1 = new Row(width);
+    auto row2 = new Row(width);
+    row1[width / 2] = true;
+
+    foreach (immutable _; 0 .. 2 ^^ nLevels) {
+        showRow(row1);
+        applyRules(row1, row2);
+        row1.swap(row2);
+    }
+}
+
+
+void main() @safe nothrow {
+    foreach (immutable i; 1 .. 6) {
+        i.showSierpinskiTriangle;
+        '\n'.putchar;
+    }
+}