Cuantos lunes tiene un año

[alvaro_trewhela]

Haría esto

Código PHP:

function weekDayOnYear($day,$year){
$md = array(31,28,31,30,31,30,31,31,30,31,30,31); //days to use
$c = 0; //counter
    for($k=0;$k<sizeof($md);$k++){ //loop for months
    $dUse = $md[$k]; //how much days for the loop
        if($k == 1 && $year%4 == 0 && (!($year%100 == 0) || $year%400 == 0)){ $dUse = 29; } //if leap year
        
        for($n=0;$n<$dUse;$n++){ //loop for days
            if(intval(date("N", strtotime("$year-".($k+1)."-".($n+1)))) == $day){ //if day
            $c++; //count
            }
        }
        
    }
return $c; //return
}
 

Donde:
year: año a verificar
day: día de la semana 1-7 de lunes a domingo

Ex:

Código PHP:

$lunes = weekDayOnYear(1,2017){
echo "2017 tiene $lunes Lunes";
 

Saludos