AOC-day3.php

<?php

$f = str_split(file('i')[0]);

$map = [
	'^' => [1,0],
	'>' => [0,1],
	'v' => [-1,0],
	'<' => [0, -1],
];

$s = $r = [[0,0]];
foreach ($f as $k => $i) {
    $p=$k%2 ? 's' : 'r' ;
    $a=end($$p);reset($$p);
    $b=$map[$i];
	array_push($$p, [$a[0]+$b[0],$a[1]+$b[1]]);
}
echo count(array_unique(array_merge($s,$r), SORT_REGULAR));