<?php 
$posted_array = array("8", "9", "12", "17");

$master_array = array("8", "9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20");

$db_input_array = array();
foreach($master_array as $p){
   if(in_array($p, $posted_array)){
      $db_input_array[$p]=1;
   }else{
      $db_input_array[$p]= 0;
   }
}

var_dump($db_input_array);

array(13) {
  [8]=>
  int(1)
  [9]=>
  int(1)
  [10]=>
  int(0)
  [11]=>
  int(0)
  [12]=>
  int(1)
  [13]=>
  int(0)
  [14]=>
  int(0)
  [15]=>
  int(0)
  [16]=>
  int(0)
  [17]=>
  int(1)
  [18]=>
  int(0)
  [19]=>
  int(0)
  [20]=>
  int(0)
}