here is my php solution arr);

for (`$i=0; $`i < `$n && $`k>0 ; $i++) { 
    if (`$arr[$`i] == `$n-$`i) {
       continue;
    }
    `$swapElement2Index = array_search($`n-`$i, $`arr);
    `$arr[$`swapElement2Index] = `$arr[$`i];
    `$arr[$`i] = `$n-$`i;
   $k--;
  }

return $arr;