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
|
--- Day 18: Settlers of The North Pole ---
On the outskirts of the North Pole base construction project, many Elves are collecting lumber.
The lumber collection area is 50 acres by 50 acres; each acre can be either [1m[97mopen ground[0m (.),
[1m[97mtrees[0m (|), or a [1m[97mlumberyard[0m (#). You take a scan of the area (your puzzle input).
Strange magic is at work here: each minute, the landscape looks entirely different. In exactly
[1m[97mone minute[0m, an open acre can fill with trees, a wooded acre can be converted to a lumberyard, or a
lumberyard can be cleared to open ground (the lumber having been sent to other projects).
The change to each acre is based entirely on [1m[97mthe contents of that acre[0m as well as [1m[97mthe number of
open, wooded, or lumberyard acres adjacent to it[0m at the start of each minute. Here, "adjacent" means
any of the eight acres surrounding that acre. (Acres on the edges of the lumber collection area
might have fewer than eight adjacent acres; the missing acres aren't counted.)
In particular:
- An [1m[97mopen[0m acre will become filled with [1m[97mtrees[0m if [1m[97mthree or more[0m adjacent acres contained trees.
Otherwise, nothing happens.
- An acre filled with [1m[97mtrees[0m will become a [1m[97mlumberyard[0m if [1m[97mthree or more[0m adjacent acres were
lumberyards. Otherwise, nothing happens.
- An acre containing a [1m[97mlumberyard[0m will remain a [1m[97mlumberyard[0m if it was adjacent to [1m[97mat least one other
lumberyard and at least one acre containing trees[0m. Otherwise, it becomes [1m[97mopen[0m.
These changes happen across all acres [1m[97msimultaneously[0m, each of them using the state of all acres at
the beginning of the minute and changing to their new form by the end of that same minute. Changes
that happen during the minute don't affect each other.
For example, suppose the lumber collection area is instead only 10 by 10 acres with this initial
configuration:
Initial state:
.#.#...|#.
.....#|##|
.|..|...#.
..|#.....#
#.#|||#|#|
...#.||...
.|....|...
||...#|.#|
|.||||..|.
...#.|..|.
After 1 minute:
.......##.
......|###
.|..|...#.
..|#||...#
..##||.|#|
...#||||..
||...|||..
|||||.||.|
||||||||||
....||..|.
After 2 minutes:
.......#..
......|#..
.|.|||....
..##|||..#
..###|||#|
...#|||||.
|||||||||.
||||||||||
||||||||||
.|||||||||
After 3 minutes:
.......#..
....|||#..
.|.||||...
..###|||.#
...##|||#|
.||##|||||
||||||||||
||||||||||
||||||||||
||||||||||
After 4 minutes:
.....|.#..
...||||#..
.|.#||||..
..###||||#
...###||#|
|||##|||||
||||||||||
||||||||||
||||||||||
||||||||||
After 5 minutes:
....|||#..
...||||#..
.|.##||||.
..####|||#
.|.###||#|
|||###||||
||||||||||
||||||||||
||||||||||
||||||||||
After 6 minutes:
...||||#..
...||||#..
.|.###|||.
..#.##|||#
|||#.##|#|
|||###||||
||||#|||||
||||||||||
||||||||||
||||||||||
After 7 minutes:
...||||#..
..||#|##..
.|.####||.
||#..##||#
||##.##|#|
|||####|||
|||###||||
||||||||||
||||||||||
||||||||||
After 8 minutes:
..||||##..
..|#####..
|||#####|.
||#...##|#
||##..###|
||##.###||
|||####|||
||||#|||||
||||||||||
||||||||||
After 9 minutes:
..||###...
.||#####..
||##...##.
||#....###
|##....##|
||##..###|
||######||
|||###||||
||||||||||
||||||||||
After 10 minutes:
.||##.....
||###.....
||##......
|##.....##
|##.....##
|##....##|
||##.####|
||#####|||
||||#|||||
||||||||||
After 10 minutes, there are 37 wooded acres and 31 lumberyards. Multiplying the number of wooded
acres by the number of lumberyards gives the total [1m[97mresource value[0m after ten minutes: 37 * 31 =
[1m[97m1147[0m.
[1m[97mWhat will the total resource value of the lumber collection area be after 10 minutes?[0m
|
