My Advent of Code solutions in Python.
kevinyap.ca/2019/12/going-fast-in-advent-of-code/
advent-of-code
python
Add solution for 2023/23
+118
+118
2023/day23.py
+118
2023/day23.py
···
1
+
import fileinput
2
+
from collections import deque, defaultdict
3
+
4
+
from utils import Point, N, S, E, W, DIRS
5
+
6
+
7
+
SLOPES = {
8
+
'^': S,
9
+
'v': N,
10
+
'<': W,
11
+
'>': E,
12
+
}
13
+
14
+
15
+
def get_neighbours(graph, node, part_2=False):
16
+
"""In part 2, we ignore slopes."""
17
+
if graph.get(node) == '#':
18
+
return
19
+
20
+
if not part_2:
21
+
if graph.get(node) in SLOPES:
22
+
yield node + SLOPES[graph.get(node)]
23
+
return
24
+
25
+
for d in DIRS:
26
+
np = node + d
27
+
if np not in graph:
28
+
continue
29
+
30
+
neighbour = graph.get(np)
31
+
32
+
if neighbour == '#':
33
+
continue
34
+
35
+
if not part_2 and neighbour in SLOPES and d != SLOPES[neighbour]:
36
+
continue
37
+
38
+
yield np
39
+
40
+
41
+
def longest_path(graph, start, end, part_2=False):
42
+
horizon = [(start, 0, set())]
43
+
best = 0
44
+
45
+
while horizon:
46
+
curr, dist, seen = horizon.pop()
47
+
48
+
if curr == end:
49
+
best = max(best, dist)
50
+
continue
51
+
52
+
if curr in seen:
53
+
continue
54
+
55
+
for neighbour, weight in graph[curr]:
56
+
horizon.append((neighbour, dist + weight, seen | set([curr])))
57
+
58
+
return best
59
+
60
+
61
+
def compress_graph(graph, part_2=False):
62
+
# Sort all points in graph by their degree.
63
+
degrees = defaultdict(set)
64
+
for node in graph:
65
+
degrees[len(list(get_neighbours(graph, node, part_2)))].add(node)
66
+
67
+
key_points = degrees[1] | degrees[3] | degrees[4]
68
+
69
+
70
+
# Find the distance from node to all other "key points" it can reach.
71
+
def bfs(start):
72
+
horizon = deque([(start, 0)])
73
+
seen = set()
74
+
75
+
while horizon:
76
+
curr, dist = horizon.pop()
77
+
78
+
if curr != start and curr in key_points:
79
+
yield curr, dist
80
+
continue
81
+
82
+
if curr in seen:
83
+
continue
84
+
85
+
seen.add(curr)
86
+
87
+
for neighbour in get_neighbours(graph, curr, part_2):
88
+
horizon.appendleft((neighbour, dist + 1))
89
+
90
+
91
+
# Create the compressed weighted graph.
92
+
compressed = defaultdict(list)
93
+
94
+
for node in key_points:
95
+
for neighbour, weight in bfs(node):
96
+
compressed[node].append((neighbour, weight))
97
+
98
+
return compressed
99
+
100
+
101
+
# Parse problem input.
102
+
GRAPH = {}
103
+
START = None
104
+
END = None
105
+
for y, line in enumerate(fileinput.input()):
106
+
for x, c in enumerate(line.strip()):
107
+
p = Point(x, y)
108
+
if c == '.':
109
+
if y == 0:
110
+
START = p
111
+
112
+
END = p
113
+
114
+
GRAPH[p] = c
115
+
116
+
print("Part 1:", longest_path(compress_graph(GRAPH), START, END))
117
+
print("Part 2:", longest_path(compress_graph(GRAPH, part_2=True), START, END, part_2=True))
118
+