answer.php

<?php

define('CELL_START', 'S');
define('CELL_GOAL', 'G');
define('CELL_WALL', '#');
define('NA', -1);

function search($sx, $sy) {
	global $maze, $visited;

	$size = count($maze);
	$moves  = [[1, 0], [-1, 0], [0, 1], [0, -1]];

	$answer = PHP_INT_MAX;
	$queue = [];

	foreach($moves as $move) {
		list($mx, $my) = $move;
		$queue[] = [$sx + $mx, $sy + $my, 1];
	}

	while(!empty($queue)) {
		list($x, $y, $step) = array_pop($queue);

		if($x < 0 || $size <= $x || $y < 0 || $size <= $y) continue;	// 枠外判定
		if($maze[$x][$y] === CELL_WALL) continue;						// 壁判定
		if($visited[$x][$y]) continue;									// 訪問済み判定

		$visited[$x][$y] = 1;

		if($maze[$x][$y] === CELL_GOAL) $answer = min($answer, $step);

		foreach($moves as $move) {
			list($mx, $my) = $move;
			$queue[] = [$x + $mx, $y + $my, $step + 1];
		}
	}

	return $answer;
}

$stdin = file_get_contents('php://stdin');
$maze = explode("\n", $stdin);

$visited = [];
for($y = 0; $y < count($maze); $y++) {
	$visited[$y] = [];
	for($x = 0; $x < strlen($maze[$y]); $x++) {
		$visited[$y][$x] = 0;
	}
}

for($x = 0; $x < count($maze); $x++) {
	for($y = 0; $y < strlen($maze[$x]); $y++) {
		if($maze[$x][$y] === CELL_START) {
			$ans = search($x, $y);
			echo ($ans === PHP_INT_MAX ? NA : $ans)."\n";
			break;
		}
	}
}

stdin

#####
#S#G#
#...#
#.#.#
#...#
#####