From 1c085ae9e52cdd3309967492c9a8316218cf7b4d Mon Sep 17 00:00:00 2001
From: Mathias Magnusson <mathias@magnusson.space>
Date: Fri, 6 Dec 2024 22:27:16 +0100
Subject: aoc2024: day 6 part 1

---
 aoc24/src/day6.zig | 136 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 136 insertions(+)
 create mode 100644 aoc24/src/day6.zig

diff --git a/aoc24/src/day6.zig b/aoc24/src/day6.zig
new file mode 100644
index 0000000..c52b0ff
--- /dev/null
+++ b/aoc24/src/day6.zig
@@ -0,0 +1,136 @@
+const std = @import("std");
+
+const Pos = @Vector(2, usize);
+
+const Dir = enum {
+    right,
+    up,
+    left,
+    down,
+
+    fn rotate(self: @This()) @This() {
+        return switch (self) {
+            .right => .down,
+            .up => .right,
+            .left => .up,
+            .down => .left,
+        };
+    }
+};
+
+const Input = struct {
+    map: std.AutoHashMap(Pos, void),
+    size: Pos,
+    start_pos: Pos,
+    start_dir: Dir,
+
+    const Self = @This();
+
+    fn step_forwards(pos: Pos, dir: Dir) ?Pos {
+        return switch (dir) {
+            .right => .{ std.math.add(usize, pos[0], 1) catch return null, pos[1] },
+            .up => .{ pos[0], std.math.sub(usize, pos[1], 1) catch return null },
+            .left => .{ std.math.sub(usize, pos[0], 1) catch return null, pos[1] },
+            .down => .{ pos[0], std.math.add(usize, pos[1], 1) catch return null },
+        };
+    }
+
+    fn step(self: Self, pos: Pos, dir: Dir) ?struct { Pos, Dir } {
+        var new_pos = Self.step_forwards(pos, dir) orelse return null;
+        var new_dir = dir;
+        while (self.map.contains(new_pos)) {
+            new_dir = new_dir.rotate();
+            new_pos = Self.step_forwards(pos, new_dir) orelse return null;
+        }
+        return .{ new_pos, new_dir };
+    }
+};
+
+pub fn parse(allocator: std.mem.Allocator, data: []const u8) !Input {
+    var lines = std.mem.split(u8, data, "\n");
+    var input = Input{ .map = std.AutoHashMap(Pos, void).init(allocator), .size = undefined, .start_pos = undefined, .start_dir = undefined };
+    var y: usize = 0;
+    while (lines.next()) |line| : (y += 1) {
+        if (line.len == 0) input.size[1] = y else input.size[0] = line.len;
+        for (0.., line) |x, c| {
+            if (c == '#') {
+                try input.map.put(.{ x, y }, {});
+            } else if (c == '>') {
+                input.start_pos = .{ x, y };
+                input.start_dir = .right;
+            } else if (c == '^') {
+                input.start_pos = .{ x, y };
+                input.start_dir = .up;
+            } else if (c == '<') {
+                input.start_pos = .{ x, y };
+                input.start_dir = .left;
+            } else if (c == 'v') {
+                input.start_pos = .{ x, y };
+                input.start_dir = .down;
+            }
+        }
+    }
+    return input;
+}
+
+fn printAndWait(input: Input, traversed: std.AutoHashMap(Pos, void)) !void {
+    var underlying_buffer: [100000]u8 = undefined;
+    var buffer = std.io.fixedBufferStream(&underlying_buffer);
+    var writer = buffer.writer();
+    for (0..input.size[1]) |y| {
+        for (0..input.size[0]) |x| {
+            try writer.print("{c}", .{
+                if (traversed.contains(.{ x, y })) 'X' else if (input.map.contains(.{ x, y })) @as(u8, '#') else '.',
+            });
+        }
+        try writer.print("\n", .{});
+    }
+    std.debug.print("{s}\n", .{underlying_buffer[0..try buffer.getPos()]});
+    try std.io.getStdIn().reader().skipUntilDelimiterOrEof('\n');
+}
+
+const test_input =
+    \\....#.....
+    \\.........#
+    \\..........
+    \\..#.......
+    \\.......#..
+    \\..........
+    \\.#..^.....
+    \\........#.
+    \\#.........
+    \\......#...
+    \\
+;
+
+test "part1" {
+    var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
+    defer arena.deinit();
+
+    const output = try part1(arena.allocator(), try parse(arena.allocator(), test_input));
+    std.debug.print("got {}\n", .{output});
+    std.debug.assert(output == 41);
+}
+
+pub fn part1(allocator: std.mem.Allocator, input: Input) !u32 {
+    var pos = input.start_pos;
+    var dir = input.start_dir;
+    var traversed = std.AutoHashMap(Pos, void).init(allocator);
+    return while (true) {
+        try traversed.put(pos, {});
+        const new = input.step(pos, dir);
+        if (new) |n| {
+            pos = n[0];
+            dir = n[1];
+            // const try printAndWait(input, traversed);
+        } else {
+            break traversed.count();
+        }
+    };
+}
+
+pub fn part2(allocator: std.mem.Allocator, input: Input) !u32 {
+    _ = allocator;
+    _ = input;
+    return 0;
+}
-- 
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