1 files changed, 84 insertions, 0 deletions
diff --git a/src/day11.zig b/src/day11.zig
new file mode 100644
index 0000000..af04ac9
--- /dev/null
+++ b/src/day11.zig
@@ -0,0 +1,84 @@
+const std = @import("std");
+const mecha = @import("mecha");
+const print = std.debug.print;
+
+pub fn solve(part: []u8, buffer: []u8, allocator: std.mem.Allocator) !void {
+    var lines = std.mem.splitScalar(u8, buffer, '\n');
+    var split = std.mem.splitScalar(u8, lines.next().?, ' ');
+
+    var numbers = std.ArrayList(usize).init(allocator);
+    defer numbers.deinit();
+    while (split.next()) |n_string| {
+        try numbers.append(try std.fmt.parseInt(usize, n_string, 10));
+    }
+
+    if (std.mem.eql(u8, part, "1")) {
+        try part1(numbers, allocator);
+    } else {
+        try part2(numbers, allocator);
+    }
+}
+
+fn digits(int: usize) usize {
+    var count: usize = 0;
+    var temp = int;
+    while (temp > 0) {
+        temp /= 10;
+        count += 1;
+    }
+    return count;
+}
+
+fn recursive(number: usize, history: *std.AutoHashMap(std.meta.Tuple(&.{ usize, usize }), usize), depth: usize) !usize {
+    if (history.get(.{ number, depth })) |value| {
+        return value;
+    }
+
+    if (depth == 0) {
+        return 1;
+    }
+
+    var sum: usize = 0;
+    if (number == 0) {
+        sum = try recursive(1, history, depth - 1);
+    } else {
+        const n_digits = digits(number);
+        if (n_digits % 2 == 0) {
+            const p = std.math.pow(usize, 10, n_digits / 2);
+            const first = number / p;
+            const second = number % p;
+
+            sum += try recursive(first, history, depth - 1);
+            sum += try recursive(second, history, depth - 1);
+        } else {
+            sum += try recursive(number * 2024, history, depth - 1);
+        }
+    }
+
+    try history.put(.{ number, depth }, sum);
+    return sum;
+}
+
+fn part1(numbers: std.ArrayList(usize), allocator: std.mem.Allocator) !void {
+    var history = std.AutoHashMap(std.meta.Tuple(&.{ usize, usize }), usize).init(allocator);
+    defer history.deinit();
+
+    var total: usize = 0;
+    for (numbers.items) |number| {
+        total += try recursive(number, &history, 25);
+    }
+
+    print("{d}\n", .{total});
+}
+
+fn part2(numbers: std.ArrayList(usize), allocator: std.mem.Allocator) !void {
+    var history = std.AutoHashMap(std.meta.Tuple(&.{ usize, usize }), usize).init(allocator);
+    defer history.deinit();
+
+    var total: usize = 0;
+    for (numbers.items) |number| {
+        total += try recursive(number, &history, 75);
+    }
+
+    print("{d}\n", .{total});
+}