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: Time Limit Exceeded)

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
//submit
//http://wisdom.sakura.ne.jp/programming/c/c58.html
//http://bituse.info/c/41
//http://rainbow.pc.uec.ac.jp/edu/program/b1/Ex2-1b.htm

//???????????¨?§?????????????
struct LIST{
    struct LIST *next;
    struct LIST *prev;
    int value;
};

//???????????????????????????
struct LIST list;

//??¢??°???????????????????????£?¨?
void my_add(int);
void my_del(int);
void my_display();
void my_release();
void my_delFirst();
void my_delLast();

int main(void){
    int n;
    int i;

    //
    list.next = &list;

    //?????°????????????????????????????????¨????????????
    list.prev = &list;

    char answer = '5';
    int figure;

    char tmp[64];
    char sep[] = " ";
    scanf("%d",&n);
    for (i = 0; i < n; i++){
        (void)getchar();
        scanf("%s",&tmp);//???????????¨??\???
        if (strcmp(tmp,"deleteFirst")==0){
            // printf("%s ",tok);
            my_delFirst();
        }else if (strcmp(tmp,"deleteLast")==0){
            // printf("%s ",tok);
            my_delLast();
        }else if (strcmp(tmp,"insert")==0){
            // printf("%s ",tok);
            (void)getchar();
            scanf("%s",&tmp);
            my_add(atoi(tmp));
            // printf("%s ",tok);
        }else if (strcmp(tmp,"delete")==0){
            // printf("%s ",tok);
            (void)getchar();
            scanf("%s",&tmp);
            my_del(atoi(tmp));
            // printf("%s ",tok);
        }else{
            // printf("??\??????????????????");
        }
        // printf("\n");
        // my_display();
        // printf("\n");
    }
    my_display();
    my_release();
    return 0;
}

void my_add(int temp){
    struct LIST *p;
    struct LIST *next;
    struct LIST *prev;

    p=(struct LIST*)malloc(sizeof(struct LIST));

    p->value=temp;
    //??????????????§???
    p->next=list.next;
    list.next->prev = p;//??????????????°??´??\?????§??§??????
    list.next = p;
    p->prev = &list;
}

void my_display(){
    if(list.next==&list){
        // puts("???????????????????????????");
        return;
    }
    struct LIST *p;
    //NULL??????????????§??¨??¨??¨???
    for(p=list.next;p!=&list;p=p->next)
    {
        if (p->next==&list){
            // printf("?????£???");
            printf("%d\n",p->value);
        }else{
        printf("%d ",p->value);
        }
    }
    // puts("");
}

void my_del(int temp){
    //??????????´??????´??????????´????????????????
    struct LIST *prev;
    prev = &list;
    struct LIST *p;
    for(p=list.next;p!=&list;p=p->next){

        if(p->value==temp){
            //?????????????´??????£????????????
            if(p->next!=&list){
                prev->next=p->next;
                p->next->prev=prev;
                free(p);
                return;
            }
            //?????????????´??????£????????????
            prev->next=&list;
            list.prev=prev;
            free(p);

            // puts("??????????????????");
            return;
        }
        prev=p;

    }
    // puts("??????????????????????????????????????§??????");

}

void my_delFirst(){
    struct LIST *p = list.next;
    if (list.next==&list)
    {
        return;
    }
    list.next = p->next;
    p->next->prev = &list;
    free(p);

}

//????????????????????°?????????????????????for?????§?????????????´??????¢?????????
void my_delLast(){
    struct LIST *p;
    struct LIST *next;
    struct LIST *prev;
    if (list.next==&list)
    {
        return;
    }
    for(p=list.next;p!=&list;p=p->next){
        prev=p;
    }
    prev->prev->next=&list;
    list.prev=prev->prev;
    free(prev);//for????????§?????????p???&list????????£???????????§prev????§£?????????
}

void my_release(){
    struct LIST *next;
    struct LIST *del;
    if (list.next==&list)
    {
        return;
    }

    next = list.next;

    while(next!=&list){
        del=next;
        next=next->next;

        free(del);
    }
}