Mine

array(2) {
  [306]=>
  int(1)
  [149]=>
  int(1)
}

    $test_array = Array();
    $test_array[306]    = 1;
    $test_array[149]    = 1;
    
    $dupes  = array_keys($test_array, 1);
    
    print_r_pre($dupes);