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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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