【PHP】取得去年同日期

例如今天是 2020.06.26(五)，是本年的第 26 週

想知道去年第 26 週的星期五是哪天

 
$dToday =  time();
$sToday = date('Y.m.d', $dToday);

$iWeek = (int) date('W', $dToday);      // 今日是本年的第幾週
$iWeekday = (int) date('w', $dToday);   // 今日是星期幾

$dLastyear1 = strtotime("1 January ".(date('Y',$dToday)-1)); // 去年第一天

$dLastyearday = strtotime("+".($iWeek-1)*7+($iWeekday-2)." day", $dLastyear1);  // 去年同週的日期
echo 'Lastyear first day == '.date('Y.m.d(w, D, 第W週)',$dLastyearday);