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++14 (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define MAX 100005
using ll =long long;
using namespace std;

struct node{
    unsigned int key;
    struct node *next;
    struct node *prev;
};

typedef struct node *NodePointer;

NodePointer nil;

NodePointer listSerch(int key){
    NodePointer t=nil->next;
    while(t!=nil){
        if(t->key==key){
            return t;
        }
        t=t->next;
    }
    return nil;
}

void init(){
    nil=new node;
    nil->next=nil;
    nil->prev=nil;
}
void printList(){
    NodePointer cur=nil->next;
    int isf=1;
    while(1){
        if(cur==nil)break;
        if(isf==0)printf(" ");
        printf("%d",cur->key);
        cur=cur->next;
        isf=0;
    }
    printf("\n");
}

void deleteNode(NodePointer t){
    if(t==nil)return;
    NodePointer temp1=t->next,temp2=t->prev;
    temp1->prev=temp2;
    temp2->next=temp1;
    delete t;
}

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 deletekey(int key){
    NodePointer t=listSerch(key);
    if(t==nil)return;
    deleteNode(t);
}

void insert(int key){
    NodePointer x=new node;
    x->key=key;
    NodePointer temp1=nil->next,temp2=nil;
    x->prev=temp2;
    x->next=temp1;
    temp1->prev=x;
    temp2->next=x;
}

int main(){
    int key,n;
    int size =0;
    char com[20];
    int np=0,nd=0;
    scanf("%d",&n);
    init();
    rep(i,n){
        scanf("%s",com);
        if(com[0]=='i'){cin>>key;insert(key);np++;size++;}
        else if(com[0]='d'){
            if(strlen(com)>6){
                if(com[6]=='F')deleteFirst();
                else if(com[6]=='L')deleteLast();
            }else{
                cin>>key;
                deletekey(key);nd++;
            }
            size--;
        }
    }
    printList();
    return 0;
}