您知道在使用PHP程式中，日曆算法是如何達成的嗎？
/**
* 日曆
*
*/
if (function_exists(‘date_default_timezone_set’)) {
date_default_timezone_set(‘Asia/Chongqing’);
}
$date = isset($_GET[‘date’]) ? $_GET[‘date’] : date(‘Y-m-d’);
$date = getdate(strtotime($date));
$end = getdate(mktime(0, 0, 0, $date[‘mon’] + 1, 1, $date[‘year’]) – 1);
$start = getdate(mktime(0, 0, 0, $date[‘mon’], 1, $date[‘year’]));
$pre = date(‘Y-m-d’, $start[0] – 1);
$next = date(‘Y-m-d’, $end[0] + 86400);
$html = ‘<table border=”1″>’;
$html .= ‘<tr>’;
$html .= ‘<td><a href=”‘ . $PHP_SELF . ‘?date=’ . $pre . ‘”>-</a></td>’;
$html .= ‘<td colspan=”5″>’ . $date[‘year’] . ‘;’ . $date[‘month’] . ‘</td>’;
$html .= ‘<td><a href=”‘ . $PHP_SELF . ‘?date=’ . $next . ‘”>+</a></td>’;
$html .= ‘</tr>’;
$arr_tpl = array(0 => ”, 1 => ”, 2 => ”, 3 => ”, 4 => ”, 5 => ”, 6 => ”);
$date_arr = array();
$j = 0;
for ($i = 0; $i < $end[‘mday’]; $i++) {
if (!isset($date_arr[$j])) {
$date_arr[$j] = $arr_tpl;
}
$date_arr[$j][($i+$start[‘wday’])%7] = $i+1;
if ($date_arr[$j][6]) {
$j++;
}
}
foreach ($date_arr as $value) {
$html .= ‘<tr>’;
foreach ($value as $v) {
if ($v) {
if ($v == $date[‘mday’]) {
$html .= ‘<td><b>’ . $v . ‘</b></td>’;
} else {
$html .= ‘<td>’ . $v . ‘</td>’;
}
} else {
$html .= ‘<td> </td>’;
}
}
$html .= ‘</tr>’;
}
$html .= ‘</table>’;
echo $html;