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
|
<?php
declare(strict_types=1);
spl_autoload_register(fn(string $className) => require "{$className}.php");
// Assumes executed from workspace root
$input = new Input('../_input/day_04.txt');
if ($input->contents === "") {
throw new RuntimeException("File not found");
}
$grid = $input->toGrid();
$matchCount = 0;
foreach ($grid->data as $y => $row) {
foreach ($row as $x => $char) {
if ($char !== 'X') {
continue;
}
$start = new Position($x, $y);
$possibleMatches = [];
$possibleMatches["north"] = $grid->getStringFromPositions([
$start,
$start->getNorth(),
$start->getNorth()->getNorth(),
$start->getNorth()->getNorth()->getNorth(),
]);
$possibleMatches["east"] = $grid->getStringFromPositions([
$start,
$start->getEast(),
$start->getEast()->getEast(),
$start->getEast()->getEast()->getEast(),
]);
$possibleMatches["south"] = $grid->getStringFromPositions([
$start,
$start->getSouth(),
$start->getSouth()->getSouth(),
$start->getSouth()->getSouth()->getSouth(),
]);
$possibleMatches["west"] = $grid->getStringFromPositions([
$start,
$start->getWest(),
$start->getWest()->getWest(),
$start->getWest()->getWest()->getWest(),
]);
$possibleMatches["north-east"] = $grid->getStringFromPositions([
$start,
$start->getNorthEast(),
$start->getNorthEast()->getNorthEast(),
$start->getNorthEast()->getNorthEast()->getNorthEast(),
]);
$possibleMatches["north-west"] = $grid->getStringFromPositions([
$start,
$start->getNorthWest(),
$start->getNorthWest()->getNorthWest(),
$start->getNorthWest()->getNorthWest()->getNorthWest(),
]);
$possibleMatches["south-east"] = $grid->getStringFromPositions([
$start,
$start->getSouthEast(),
$start->getSouthEast()->getSouthEast(),
$start->getSouthEast()->getSouthEast()->getSouthEast(),
]);
$possibleMatches["south-west"] = $grid->getStringFromPositions([
$start,
$start->getSouthWest(),
$start->getSouthWest()->getSouthWest(),
$start->getSouthWest()->getSouthWest()->getSouthWest(),
]);
$matchCount += array_reduce(
array: $possibleMatches,
callback: fn(int $acc, string $possibleMatch): int => match ($possibleMatch) {
"XMAS" => $acc + 1,
default => $acc,
},
initial: 0,
);
}
}
// ANSWER: 2517
echo $matchCount;
|
