part02.php

<?php

global $data;
$og = $data;

$newdata = array();

for ($ty = 0; $ty < 5; $ty++) {
    if ($ty == 0) {
        $tilerow = &$data;
    } else {
        $tilerow = array();
    }
    for ($tx = 0; $tx < 5; $tx++) {
        $offset = $ty + $tx;
        if ($offset == 0) {
            continue;
        }

        foreach ($og as $y => &$row) {
            if (empty($tilerow[$y])) {
                $tilerow[$y] = array();
            }
            foreach ($row as $x => &$ele) {
                $val = $ele + $offset;
                if ($val > 9) {
                    $val = $val % 10 + 1;
                }
                $tilerow[$y][] = $val;
            }
        }
    }
    $newdata = array_merge($newdata, $data);
}

$data = &$newdata;

$costs = array_fill(0, count($data), array_fill(0, count($data[0]), PHP_INT_MAX));

$costs[0][0] = 0;

$changed = true;
while ($changed) {
    $changed = false;
    foreach ($costs as $y => &$row) {
        foreach ($row as $x => &$ele) {
            $base = $data[$x][$y];
            if ($y > 0 && $costs[$y-1][$x] + $base < $ele) {
                $changed = true;
                $ele = $costs[$y-1][$x] + $base;
            }
            if ($y < count($costs) - 1 && $costs[$y+1][$x] + $base < $ele) {
                $changed = true;
                $ele = $costs[$y+1][$x] + $base;
            }
            if ($x > 0 && $costs[$y][$x-1] + $base < $ele) {
                $changed = true;
                $ele = $costs[$y][$x-1] + $base;
            }
            if ($x < count($row) - 1 && $costs[$y][$x+1] + $base < $ele) {
                $changed = true;
                $ele = $costs[$y][$x+1] + $base;
            }
        }
    }
}

$cost = $costs[count($costs)-1][count($costs[0])-1];
?>
The cost is <?php echo $cost; ?>.
<?php /* vim: set expandtab tabstop=4 smarttab shiftwidth=4: */ ?>