Algorithm 2 Compactify List

Input: doubly linked list $L$ and $F$ stored in multiple arrays $free$ , $prev$ and $next$

1:procedure SwapObject( $i, j$ )

2:Swap( $next[prev[i]], next[prev[j]]$ )

3:Swap( $prev[next[i]], prev[next[j]]$ )

4:Swap( $prev[i], prev[j]$ )

5:Swap( $next[i], next[j]$ )

6:Swap( $key[i], key[j]$ )

7:end procedure

9: $x = L.head$

10: $i = 1$

11:while $x \ne NIL$ do

12:SwapObject( $i, x$ )

13:if $F.head = i$ then

14: $F.head = x$

15:end if

16: $x = next[i]$

17: $i = i + 1$

18:end while

19: $L.head = 1$