From 27aa24f5038124def8c41dcbf1d44e6ccf6d3881 Mon Sep 17 00:00:00 2001
From: Dustin Swan <dustin@dustinswan.com>
Date: Fri, 15 Dec 2023 14:10:45 -0700
Subject: [PATCH] Day 15. So random this year. Fricking AIs

---
 day15/main.zig | 115 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 115 insertions(+)
 create mode 100644 day15/main.zig

diff --git a/day15/main.zig b/day15/main.zig
new file mode 100644
index 0000000..d96b228
--- /dev/null
+++ b/day15/main.zig
@@ -0,0 +1,115 @@
+const std = @import("std");
+
+const Lens = struct { label: []const u8, focalLength: u8 };
+
+pub fn main() !void {
+    var content = @embedFile("data.txt");
+
+    var words = std.mem.split(u8, content, ",");
+
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = gpa.allocator();
+
+    var boxes = std.AutoHashMap(u32, std.ArrayList(Lens)).init(allocator);
+    defer boxes.deinit();
+
+    var part1: u32 = 0;
+    while (words.next()) |w| {
+        // stupid last char thing
+        const word = if (w[w.len - 1] == 10) w[0 .. w.len - 2] else w;
+
+        // Part 1
+        part1 += hash(word);
+
+        // Part 2
+        const dash = std.mem.indexOf(u8, word, "-");
+        const equals = std.mem.indexOf(u8, word, "=");
+        const idx = dash orelse equals orelse unreachable;
+        const label = word[0..idx];
+        const box = hash(label);
+        std.debug.print("\nAfter \"{s}\":\n", .{word});
+
+        if (dash != null) {
+            // if dash, find the box
+            if (boxes.getPtr(box)) |list| {
+                // get the list, and find a lens with this label in it
+                var indexToRemove: ?usize = null;
+                for (list.items, 0..) |l, i| {
+                    if (std.mem.eql(u8, l.label, label)) {
+                        indexToRemove = i;
+                    }
+                }
+
+                // if it's there, remove it
+                if (indexToRemove) |i| {
+                    _ = list.orderedRemove(i);
+                }
+            }
+        } else {
+            // if equals, parse out parts, put it in the box
+            const focalLength = try std.fmt.parseInt(u8, word[idx + 1 ..], 10);
+            const lens = Lens{ .focalLength = focalLength, .label = label };
+
+            // does this list exist? use it. otherwise make a new one
+            var list = boxes.get(box) orelse std.ArrayList(Lens).init(allocator);
+
+            // find if this lens is already in the list
+            var dupIdx: ?usize = null;
+            for (list.items, 0..) |l, i| {
+                if (std.mem.eql(u8, l.label, label)) {
+                    dupIdx = i;
+                }
+            }
+
+            // if it is, replace it with the new lens
+            if (dupIdx) |i| {
+                try list.replaceRange(i, 1, &[_]Lens{lens});
+            } else {
+                try list.append(lens);
+            }
+            try boxes.put(box, list);
+        }
+
+        printBoxes(boxes);
+    }
+
+    std.debug.print("Part 1: {d}\n", .{part1});
+
+    var part2: usize = 0;
+    var it = boxes.iterator();
+    while (it.next()) |box| {
+        const boxNumber = box.key_ptr.*;
+
+        for (box.value_ptr.items, 0..) |lens, slotNumber| {
+            part2 += (boxNumber + 1) * (slotNumber + 1) * lens.focalLength;
+        }
+    }
+
+    std.debug.print("Part 2: {d}\n", .{part2});
+}
+
+fn hash(word: []const u8) u32 {
+    var sum: u32 = 0;
+    for (word) |c| {
+        if (c == 10) {
+            break;
+        }
+        sum += c;
+        sum *= 17;
+        sum = sum % 256;
+    }
+
+    return sum;
+}
+
+fn printBoxes(boxes: std.AutoHashMap(u32, std.ArrayList(Lens))) void {
+    var it = boxes.iterator();
+    while (it.next()) |list| {
+        std.debug.print("Box {d}: ", .{list.key_ptr.*});
+
+        for (list.value_ptr.items) |lens| {
+            std.debug.print("[{s} {d}] ", .{ lens.label, lens.focalLength });
+        }
+        std.debug.print("\n", .{});
+    }
+}