day3.php

<?php 

$i = file_get_contents('i');
//$i = '^>v<';
$x = $rx = 0;
$y = $ry = 0;
foreach (str_split($i) as $n => $dir) {
    switch ($dir) {
        case '^':
            ($n % 2 == 0) ? $x++ : $rx++;
            break;
        case '<':
            ($n % 2 == 0) ? $y-- : $ry--;
            break;
        case '>':
            ($n % 2 == 0) ? $y++ : $ry++;
            break;
        default:
            ($n % 2 == 0) ? $x-- : $rx--;
    }
    ($n % 2 == 0) ? $arr[0][$n] = "$x,$y" : $arr[1][$n] = "$rx,$ry";
}

$s = count(array_unique($arr[0]));
$r = count(array_unique($arr[1]));

echo "santa: ".$s.PHP_EOL;
echo "robo: ".$r.PHP_EOL;

echo "Total: ". (count(array_unique(array_merge($arr[0], $arr[1])))+1);