Solved day 6 part 1. Part 2 looks scarier

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

inputs/day06.example.txt

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inputs/day06.txt

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src/day06.zig

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+const std = @import("std");
+const fmt = std.fmt;
+const print = std.debug.print;
+const args = @import("lib/args.zig");
+const files = @import("lib/files.zig");
+
+const Tile = enum {
+    Unvisited,
+    Visited,
+    Obstacle,
+};
+
+const Direction = enum(u2) {
+    Up,
+    Right,
+    Down,
+    Left,
+};
+
+const Guard = struct {
+    direction: Direction = .Up,
+    x: usize,
+    y: usize,
+
+    fn rotate(self: *Guard) void {
+        self.direction = @enumFromInt(@addWithOverflow(1, @intFromEnum(self.direction))[0]);
+    }
+
+    fn walk(self: *Guard, map: *[130][130]Tile, size: usize) ?bool {
+        var new_x = self.x;
+        var new_y = self.y;
+        switch (self.direction) {
+            .Up => {
+                if (self.y == 0) {
+                    return null;
+                }
+                new_y -= 1;
+            },
+            .Right => {
+                if (self.x == size - 1) {
+                    return null;
+                }
+                new_x += 1;
+            },
+            .Down => {
+                if (self.y == size - 1) {
+                    return null;
+                }
+                new_y += 1;
+            },
+            .Left => {
+                if (self.x == 0) {
+                    return null;
+                }
+                new_x -= 1;
+            },
+        }
+
+        switch (map[new_y][new_x]) {
+            .Unvisited => {
+                self.x = new_x;
+                self.y = new_y;
+                map[new_y][new_x] = .Visited;
+                return true;
+            },
+            .Visited => {
+                self.x = new_x;
+                self.y = new_y;
+                return false;
+            },
+            .Obstacle => {
+                // This will overflow the stack if the guard is surrounded
+                // by obstacles, should not happen for the inputs we have.
+                self.rotate();
+                return self.walk(map, size);
+            },
+        }
+        unreachable;
+    }
+};
+
+fn printMap(map: [130][130]Tile, size: usize) void {
+    for (0..size) |y| {
+        for (0..size) |x| {
+            const print_char: u8 = switch (map[y][x]) {
+                .Visited => 'X',
+                .Unvisited => '.',
+                .Obstacle => '#',
+            };
+            print("{c}", .{print_char});
+        }
+        print("\n", .{});
+    }
+}
+
+// walkMap walks the guard along the map until they exit, and returns
+// the number of unique, unvisited tiles they walked along.
+fn walkMap(map: *[130][130]Tile, size: usize, guard: *Guard) usize {
+    var unique_visited_tiles: usize = 0;
+    while (guard.walk(map, size)) |new_tile| {
+        if (new_tile) {
+            unique_visited_tiles += 1;
+        }
+    }
+    return unique_visited_tiles;
+}
+
+pub fn main() !void {
+    const input_path = args.getFirstArg();
+    const input = try files.openForReading(input_path);
+
+    var map: [130][130]Tile = .{.{.Unvisited} ** 130} ** 130;
+    var map_size: usize = undefined;
+
+    var line_buf: [131]u8 = undefined;
+    var guard = Guard{
+        .x = undefined,
+        .y = undefined,
+    };
+    var y: usize = 0;
+    var visited_tiles: usize = 0;
+    while (files.readLine(input, &line_buf)) |line| {
+        defer y += 1;
+        map_size = line.len;
+        for (line, 0..) |tile, x| {
+            if (tile == '^') {
+                guard.x = x;
+                guard.y = y;
+                map[y][x] = .Visited;
+                visited_tiles += 1;
+            } else if (tile == '#') {
+                map[y][x] = .Obstacle;
+            }
+        }
+    } else |err| {
+        print("Done reading input with error: {any}\n", .{err});
+    }
+
+    visited_tiles += walkMap(&map, map_size, &guard);
+    printMap(map, map_size);
+    print("Visited tiles: {d}\n", .{visited_tiles});
+}