Ordenar registros con php

$a = array("1"=>"1","2"=>"2","3"=>"3","4"=>"4","5"=>"5");
$b = array("4"=>"2");
print_r(ordenar($a,$b));
//Array ( [4] => 2 [2] => 3 [3] => 4 )
function ordenar($a=array(),$b=array()){
	$c = array();
	//1.QUE ESTEN ORDENADO POR VALOR DE MENOR A MAYOR
	asort($a);
	asort($b);
	//2.QUE EXISTA EL INDICE A CAMBIAR
	if (array_key_exists(key($b), $a)) {
		$k = key($b);
		$v = current($b);
		if($a[$k] != $v){//3. COMPROBAR SI NO EXISTE VALOR EN ARRAY ORIGINAL
			//4. REVERTIR EL ORDEN
			$a2 = array_reverse($a, true);
			//5. SI EL VALUE A CAMBIAR ES MENOR
			if($v < $a[$k]){
				foreach($a2 as $k3=>$v3){
					if($v3 == $a[$k]){
						$c[$k3] = $v;
					}elseif($v3 >= $v and $v3 < $a[$k] ){
						$c[$k3] = $v3 + 1;
					}
				}
			}
			//6. SI EL VALUE A CAMBIAR ES MAYOR
			if($v > $a[$k]){
				foreach($a2 as $k3=>$v3){
					if($v3 == $a[$k]){
						$c[$k3] = $v;
					}elseif($v3 > $a[$k] and $v3 <= $v ){
						$c[$k3] = $v3 - 1;
					}
				}
			}
 
		}
	}else{// SI NO EXISTE EL INDICE A CAMBIAR
		$k = key($b);
		$v = current($b);
		$a2 = $a;
		if(array_search($v,$a)){
			$i = 0;
			$e = 0;
			foreach($a2 as $k3=>$v3){
				if($e == 0 && $v3 == $v){
					$c[$k3] = $v + 1 ;
					$e = 1;
					$i++;
				}elseif($e == 1 && $v3 == $v + $i){
					$c[$k3] = $v + $i + 1 ;
					$i++;
				}
			}
			$c[$k] = $v;
		}else{
			$c[$k] = $v;
		}
	}
	asort($c);
	return $c;
}