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>
struct node {
	int key;
	struct node *next;
	struct node *prev;
};
typedef struct node *nodepointer;
nodepointer head;
nodepointer tail;
int juage(char *);
void delete(int );
void deleteFirst(void);
void deleteLast(void);
void insert(int );
void init(void);
void print(void);
int main(){
	int i,j,n,data;
	char order[15];
	init();
	scanf("%d",&n);
	for(i=0; i<n; i++){
		scanf("%s",order);
		switch(juage(order)){
			case 1:
	//			printf("1");
				scanf("%d",&data);
				insert(data);
				break;
			case 2:
	//			printf("2");
				scanf("%d",&data);
				delete(data);
				break;
			case 3:
				deleteFirst();
				break;
			case 4:
				deleteLast();
				break;
		}
	}
	print();
	return 0;
}

void deleteLast(){
	nodepointer tmp;
	tmp = tail->prev->prev;
	tmp->next = tail;
	tail->prev = tmp;
}

void deleteFirst(){
	nodepointer tmp;
	tmp = head->next->next;
	tmp->prev = head;
	head->next = tmp;
}

void delete(int key){
	nodepointer i,tmp;
	for(i = head; i != tail; i = i->next){
		if(i->next->key == key){
			tmp = i->next->next;
			tmp->prev = i;
			i->next = tmp;
			break;
		}
	}
}

void insert(int key){
	nodepointer tmp;
	tmp = malloc(sizeof(struct node));
	tmp->key = key;
	head->next->prev = tmp;
	tmp->next = head->next;
	head->next = tmp;
	tmp->prev = head;
}
void print(void){
	nodepointer i;
	//	printf("%d ",head->next->key);
	for(i = head->next; i != tail; i = i->next){
		//printf("a");
		i->next != tail ? printf("%d ",i->key) : printf("%d\n",i->key);
	}
	
}

int juage(char *order){
	char str1[]="insert";
	char str2[]="delete";
	char str3[]="deleteFirst";
	char str4[]="deleteLast";
	if(strcmp(order,str1) == 0)return 1;
	if(strcmp(order,str2) == 0)return 2;
	if(strcmp(order,str3) == 0)return 3;
	if(strcmp(order,str4) == 0)return 4;
}
void init(void){
	head = malloc(sizeof(struct node));
	tail = malloc(sizeof(struct node));
	head->key = -1;
	tail->key = -2;
	head->next = tail;
	tail->prev = head;
}