1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
|
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 Map = struct {
obstacles: std.AutoHashMap(Pos, void),
size: Pos,
const Self = @This();
fn step_forwards(self: Self, pos: Pos, dir: Dir) ?Pos {
return switch (dir) {
.right => .{ if (pos[0] + 1 == self.size[0]) return null else pos[0] + 1, 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], if (pos[1] + 1 == self.size[1]) return null else pos[1] + 1 },
};
}
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.obstacles.contains(new_pos)) {
new_dir = new_dir.rotate();
new_pos = self.step_forwards(pos, new_dir) orelse return null;
}
return .{ new_pos, new_dir };
}
};
const Input = struct {
map: Map,
start_pos: Pos,
start_dir: Dir,
};
pub fn parse(allocator: std.mem.Allocator, data: []const u8) !Input {
var lines = std.mem.split(u8, data, "\n");
var input = Input{
.map = .{
.obstacles = 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.map.size[1] = y else input.map.size[0] = line.len;
for (0.., line) |x, c| {
if (c == '#') {
try input.map.obstacles.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(map: Map, 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..map.size[1]) |y| {
for (0..map.size[0]) |x| {
writer.print("{c}", .{
if (traversed.contains(.{ x, y })) 'X' else if (map.obstacles.contains(.{ x, y })) @as(u8, '#') else '.',
}) catch unreachable;
}
writer.print("\n", .{}) catch unreachable;
}
var keys = traversed.keyIterator();
while (keys.next()) |pos| {
if (@reduce(.Or, pos.* >= map.size)) {
writer.print("oob: {}\n", .{pos.*}) catch unreachable;
}
}
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);
defer printAndWait(input.map, traversed);
return while (true) {
try traversed.put(pos, {});
const new = input.map.step(pos, dir);
if (new) |n| {
pos = n[0];
dir = n[1];
// try printAndWait(input.map, traversed);
} else {
break traversed.count();
}
};
}
test "part2" {
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
const output = try part2(arena.allocator(), try parse(arena.allocator(), test_input));
std.debug.print("got {}\n", .{output});
std.debug.assert(output == 6);
}
pub fn part2(allocator: std.mem.Allocator, input: Input) !u32 {
var pos = input.start_pos;
var dir = input.start_dir;
var options = std.AutoHashMap(Pos, void).init(allocator);
var traversed = std.AutoHashMap(Pos, void).init(allocator);
var map: Map = .{ .obstacles = try input.map.obstacles.clone(), .size = input.map.size };
return while (true) {
try traversed.put(pos, {});
const next = map.step(pos, dir) orelse break options.count();
defer pos = next[0];
defer dir = next[1];
const next_pos = next[0];
if (map.obstacles.contains(next_pos) or traversed.contains(next_pos)) continue;
try map.obstacles.put(next_pos, {});
if (try gets_stuck(allocator, map, pos, dir)) {
try options.put(next_pos, {});
}
std.debug.assert(map.obstacles.remove(next_pos));
};
}
fn gets_stuck(allocator: std.mem.Allocator, map: Map, start_pos: Pos, start_dir: Dir) !bool {
var pos = start_pos;
var dir = start_dir;
var traversed = std.AutoHashMap(struct { Pos, Dir }, void).init(allocator);
defer traversed.deinit();
return while (true) {
const res = try traversed.getOrPut(.{ pos, dir });
if (res.found_existing) break true;
const new = map.step(pos, dir);
if (new) |n| {
pos = n[0];
dir = n[1];
// try printAndWait(input.map, traversed);
} else {
break false;
}
};
}
|
