https://codeiq.jp/q/3085

santa.php

<?php
$arr = array(); $maxx = $maxy = 0;
while($line=fgets(STDIN)){
	$buf = trim($line).PHP_EOL;
	list($x, $y) = explode(",", $buf);
	$arr[] = $buf;
	$maxx = max((int)$x,$maxx); $maxy = max((int)$y,$maxy);
}
$minx = $maxx; $miny = $maxy;
foreach($arr as $buf) {
	list($x, $y) = explode(",", $buf);
	$minx = min((int)$x,$minx); $miny = min((int)$y,$miny);
}
$a = max(($maxx - $minx), ($maxy - $miny));
echo ($a * $a) . "\n";