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<stdlib.h>
#include<string.h>

struct node{
  unsigned int key;//keyを格納
  struct node *next;//次のキューの位置を格納（先頭の場合はnil）
  struct node *prev;//前のキューの位置を格納（末尾の場合はnil）
};

typedef struct node * NodePointer;

NodePointer nil;

NodePointer listSearch(int key){
  /* your code */
  int i=0;
  NodePointer x,y=NULL;
  for(x=nil->prev;;x=x->next){
  	if(x->key==key) y=x;
  	if(x->next==nil) break;
  }
  //printf("%d\n",y->key);
  return y;
}

void init(){//キューの先頭と末尾の位置を格納
  nil = malloc(sizeof(struct node));
  nil->next = nil;//first
  nil->prev = nil;//last
  nil->key = -1;
}

void printList(int n){//キューに格納されているkeyを出力
  NodePointer cur = nil->prev;
  int i = 1,p;
  int box[n];
  int next[n],prev[n];
  for(i=0;;i++){
    box[i]=cur->key;
    next[i]=cur->next->key;
    prev[i]=cur->prev->key;
    if ( nil == cur->next ) break;
    cur = cur->next;
  }
  p=i;
  for(;i>-1;i--){
  	printf("%d",box[i]);
  	if(i!=0) printf(" ");
  }
  printf("\n");
}

void deleteNode(NodePointer t){//削除するキューの位置によって処理を分岐
  if(t->next==nil){//先頭の場合
    t->prev->next=nil;
    nil->next=t->prev;
    if(t->prev==nil) nil->prev=nil;
  }else if(t->prev==nil){//末尾の場合
  	nil->prev=t->next;
  	t->next->prev=nil;
  }else{//それ以外
  	t->prev->next=t->next;
    t->next->prev=t->prev;
  }
}

void deleteFirst(){
  NodePointer t = nil->next;
  if ( t == nil ) return;
  deleteNode(t);
}

void deleteLast(){
   NodePointer t=nil->prev;
   if ( t == nil ) return;
   deleteNode(t);}

void delete(int key){
  NodePointer t;
  t=listSearch(key);
  if(t!=NULL) deleteNode(t);
}


void insert(int key){
  NodePointer x;
  x = malloc(sizeof(struct node));
  x->key = key;
  if(nil->prev==nil){
  	nil->prev=x;
  	x->prev=nil;
  }else{
  	x->prev=nil->next;
  	x->prev->next=x;
  }
  x->next=nil;
  nil->next=x;
}

int main(){
  int key, n, i;
  int size = 0;//scanfした命令数
  char com[20];
  scanf("%d", &n);
  init();  
  for ( i = 0; i < n; i++ ){
    scanf("%s", com);
    if ( com[0] == 'i' ) {scanf("%d",&key);insert(key);}//insert
    else if ( com[0] == 'd' ) {//deretegroup
      if (strlen(com) > 6){//deletefirst or delete last
		if ( com[6] == 'F' ) {;deleteFirst();}
		else if ( com[6] == 'L' ) {deleteLast();}
      	}else {
      		scanf("%d",&key);
			delete(key);// delete x
      	}
    }
  }

  printList(n);
  return 0;
}