A-M baby

Task/Happy-numbers/D/happy-numbers-1.d

@@ -0,0 +1,23 @@
+import std.stdio, std.algorithm, std.range;
+
+bool isHappy(int n) pure nothrow {
+    int[int] past;
+
+    while (true) {
+        int total = 0;
+        while (n > 0) {
+            total += (n % 10) ^^ 2;
+            n /= 10;
+        }
+        if (total == 1)
+            return true;
+        if (total in past)
+            return false;
+        n = total;
+        past[total] = 0;
+    }
+}
+
+void main() {
+    int.max.iota().filter!isHappy().take(8).writeln();
+}

Task/Happy-numbers/D/happy-numbers-2.d

@@ -0,0 +1,19 @@
+import std.stdio, std.algorithm, std.range, std.conv;
+
+bool isHappy(int n) /*pure nothrow*/ {
+    int[int] seen;
+
+    while (true) {
+        const t = n.text().map!q{(a - '0') ^^ 2}().reduce!q{a + b}();
+        if (t == 1)
+            return true;
+        if (t in seen)
+            return false;
+        n = t;
+        seen[t] = 0;
+    }
+}
+
+void main() {
+    int.max.iota().filter!isHappy().take(8).writeln();
+}