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 <string.h>
#include <stdio.h>
#include <stdlib.h>
struct Node {
    int key;
    struct Node *prev;
	struct Node *next;
};
  
struct Node *note;
  
void init() {
    note = (struct Node *)malloc(sizeof(struct Node));
    note->next = note;
    note->prev = note;
}
  
void insert(int key) {
    struct Node *x = (struct Node *)malloc(sizeof(struct Node));
    x->key = key;
	note->next->prev = x;
    x->next = note->next;
    note->next = x;
    x->prev = note;
}
  
struct Node* listSearch(int key) {
    struct Node *cur = note->next;
    while(cur != note && cur->key != key ) {
        cur = cur-> next;
    }
    return cur;
}
  
void deleteNode(struct Node *t) {
    if (t == note) return;
    t->prev->next = t->next;
    t->next->prev = t->prev;
    free(t);
}
  
void deleteFirst() {
    deleteNode(note->next);
}
  
void deleteLast() {
    deleteNode(note->prev);
}
void deleteKey(int key) {
    deleteNode(listSearch(key));
}
  
void printList() {
    struct Node *cur;
    cur = note->next;
    int isf = 0;
  
    while(1) {
        if (cur == note) break;
        if(isf++ > 0) printf(" ");
        printf("%d", cur->key);
        cur = cur->next;
    }
    printf("\n");
}
  
  
int main(void) {
    int key, n;
    char order[20];
    scanf("%d", &n);
    init();
    for (int i = 0; i < n; i++) {
        scanf("%s%d",order, &key);
        if(order[0] == 'i') {
            insert(key);
        }else if(order[0] == 'd') {
            if(strlen(order) > 6) {
                if( order[6] == 'F') {
                    deleteFirst();
                }else if(order[6] == 'L') {
                    deleteLast();
                }
            }else {
                deleteKey(key);
            }
        }
    }
    printList();
    return 0;
}