Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in C (judge verdict: Accepted)

#include <stdio.h>
#include <string.h>

int main(void){
  int n,i,j,k,x,key[2000000],s,l=1,f;
  char com[20];
  k=0;
  scanf("%d",&n);
  for(i=1;i<=n;i++){
    scanf("%s",com);
    if(strcmp(com,"insert")==0){
      scanf("%d",&x);
      k++;
      key[k]=x;
      f=k;
    }
    else if(strcmp(com,"delete")==0){
      scanf("%d",&x);
      for(j=k;j>=1;j--){
	if(key[j]==x){
	  key[j]=-1;
	  break;
	}
      }
    }
    else if(strcmp(com,"deleteFirst")==0){
      for(j=f;j>=1;j--){
	if(key[j]!=-1){
	  key[j]=-1;
	  f=j;
	  break;
	}
      }
    }
    else if(strcmp(com,"deleteLast")==0){
      for(j=l;j<=k;j++){
	if(key[j]!=-1){
	  key[j]=-1;
	  l=j;
	  break;
	}
      }
    }
  }
  for(i=k;i>=1;i--){
    if(key[i]!=-1) s=i;
  }
  for(i=k;i>=s;i--){
    if(key[i]!=-1){
      printf("%d",key[i]);
      if(i>s) printf(" ");
    }
  }
  printf("\n");
  return 0;
}