输入第几周获取在该年的日期

方法一

function GetWeekDate($week){
    date_default_timezone_set('PRC');
    $year = 2016;//哪年
    $week = $week;//第几周
    $day = 1;//星期几

    $last_year = strtotime(($year-1).'-12-31');
    $last_date_lase_year_in_week = date('N',$last_year);
    $days = ($week - 1) * 7 + $day - $last_date_lase_year_in_week;
    $the_day = strtotime("+$days days",$last_year);
    echo date('Y-m-d',$the_day);
}

方法二

function get_week($year) {
    $year_start = $year . "-01-01";
    $year_end = $year . "-12-31";
    $startday = strtotime($year_start);
    if (intval(date('N', $startday)) != '1') {
        $startday = strtotime("next monday", strtotime($year_start)); //获取年第一周的日期
    }
    $year_mondy = date("Y-m-d", $startday); //获取年第一周的日期

    $endday = strtotime($year_end);
    if (intval(date('W', $endday)) == '7') {
        $endday = strtotime("last sunday", strtotime($year_end));
    }

    $num = intval(date('W', $endday));
    for ($i = 1; $i <= $num; $i++) {
        $j = $i -1;
        $start_date = date("Y-m-d", strtotime("$year_mondy $j week "));

        $end_day = date("Y-m-d", strtotime("$start_date +6 day"));

        $week_array[$i] = array (
        str_replace("-", ".", $start_date ), str_replace("-", ".", $end_day));
    }
    echo '<pre>';
    print_r($week_array);
}