Data update

Task/Department-numbers/Zig/department-numbers-3.zig

@@ -1 +1,73 @@
 const std = @import("std");
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+
+    try stdout.writeAll("Police  Sanitation  Fire\n");
+    try stdout.writeAll("------  ----------  ----\n");
+
+    var it = SolutionIterator.init();
+    while (it.next()) |solution| {
+        try stdout.print(
+            "  {d}         {d}         {d}\n",
+            .{ solution.police, solution.sanitation, solution.fire },
+        );
+    }
+}
+
+/// 3 bit unsigned (u3) limits 0 <= department <= 7
+const Departments = packed struct {
+    police: u3,
+    sanitation: u3,
+    fire: u3,
+};
+
+const DepartmentsUnion = packed union {
+    departments: Departments,
+    together: u9,
+};
+
+const SolutionIterator = struct {
+    // police is initialized to one as adding one is the first operation in next()
+    // with the result .police == 2 (an even number) on the first pass.
+    u: DepartmentsUnion = .{ .departments = .{ .police = 1, .sanitation = 1, .fire = 1 } },
+
+    /// init() returns an initialised structure.
+    /// Using init() is a common Zig pattern.
+    fn init() SolutionIterator {
+        return SolutionIterator{};
+    }
+
+    fn next(self: *SolutionIterator) ?Departments {
+        if (self.u.together == 0) return null; // already completed
+
+        while (true) {
+            const ov = @addWithOverflow(self.u.together, 1);
+            if (ov[1] == 1) {
+                self.u.together = 0;
+                return null; // overflowed, completed
+            } else {
+                self.u.together = ov[0];
+                // None can be zero
+                if (self.u.departments.police == 0) self.u.departments.police = 2; // even
+                if (self.u.departments.sanitation == 0) self.u.departments.sanitation = 1;
+                if (self.u.departments.fire == 0) self.u.departments.fire = 1;
+                // Police must be even
+                if (self.u.departments.police & 1 == 1)
+                    continue;
+                // No two can be the same
+                if (self.u.departments.police == self.u.departments.sanitation) continue;
+                if (self.u.departments.sanitation == self.u.departments.fire) continue;
+                if (self.u.departments.fire == self.u.departments.police) continue;
+                // Must total twelve (maximum sum 7 + 7 + 7 = 21 requires 5 bits)
+                const p = @as(u5, self.u.departments.police);
+                const s = @as(u5, self.u.departments.sanitation);
+                const f = @as(u5, self.u.departments.fire);
+                if (p + s + f != 12)
+                    continue;
+
+                return self.u.departments;
+            }
+        }
+    }
+};

Task/Department-numbers/Zig/department-numbers-4.zig

@@ -1,14 +0,0 @@
-pub fn main() !void {
-    const stdout = std.io.getStdOut().writer();
-
-    try stdout.writeAll("Police  Sanitation  Fire\n");
-    try stdout.writeAll("------  ----------  ----\n");
-
-    var it = SolutionIterator{};
-    while (it.next()) |solution| {
-        try stdout.print(
-            "  {d}         {d}         {d}\n",
-            .{ solution.police, solution.sanitation, solution.fire },
-        );
-    }
-}

Task/Department-numbers/Zig/department-numbers-5.zig

@@ -1,32 +0,0 @@
-const SolutionIterator = struct {
-    // 5 bit unsigned (u5) allows addition up to 31
-    p: u5 = 2,
-    s: u5 = 1,
-    f: u5 = 0,
-
-    /// 3 bit unsigned (u3) limits 0 <= department <= 7
-    fn next(self: *SolutionIterator) ?struct { police: u3, sanitation: u3, fire: u3 } {
-        if (self.p > 7) return null; // already completed
-
-        while (true) {
-            self.f += 1; // fire
-            if (self.f > 7) {
-                self.f = 1;
-                self.s += 1; // sanitation
-                if (self.s > 7) {
-                    self.s = 1;
-                    self.p += 2; // police
-                    if (self.p > 7) {
-                        return null; // completed
-                    }
-                }
-            }
-            if (self.p + self.f + self.s == 12)
-                return .{
-                    .police = @truncate(self.p),
-                    .sanitation = @truncate(self.s),
-                    .fire = @truncate(self.f),
-                };
-        }
-    }
-};