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 "stdlib.h"
#include "stdio.h"
#include "string.h"

struct NODE{
    int key;
    struct NODE *prev, *next;
};

struct NODE *head;

void init(){
    head = (struct NODE*)malloc(sizeof(struct NODE));
    head->next = head;
    head->prev = head;
}

void insert(int x){
    struct NODE *temp = (struct NODE*)malloc(sizeof(struct NODE));
    temp->key = x;
    temp->next = head->next;
    head->next->prev = temp;
    head->next = temp;
    temp->prev = head; 
}

struct NODE* listSearch(int x){
    struct NODE *cur = head->next;
    while(cur != head && cur->key != x){
        cur = cur->next;
    }
    return cur;
}

void deleteNode(struct NODE *deleNode){
    if(deleNode == head){
        return;
    }
    deleNode->prev->next = deleNode->next;
    deleNode->next->prev = deleNode->prev;
}

void delete(int x){
    deleteNode(listSearch(x));
}

void deleteFirst(void){
    deleteNode(head->next);
}

void deleteLast(void){
    deleteNode(head->prev);
}

int N;
char ins[10];
int opNum;


int main(){
    //freopen("DoublyLinkedList.txt", "r", stdin);
    init();
    scanf("%d", &N);
    for(int i=0; i<N; i++){
        scanf("%s", ins);
        if(strcmp(ins, "insert") == 0)
        {
            scanf("%d", &opNum);
            insert(opNum);
        }
        else if(strcmp(ins, "delete") == 0){
            scanf("%d", &opNum);
            delete(opNum);
        }
        else if(strcmp(ins, "deleteFirst") == 0){
            deleteFirst();
        }
        else{
            deleteLast();
        }
    }
    struct NODE *cur = head->next;
    while(cur != head->prev){
        printf("%d ", cur->key);
        cur = cur->next;
    }
    printf("%d\n", cur->key);
}