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 <stdlib.h>

void insert(int _value);
void delete(int _value);
void deleteFirst(void);
void deleteLast(void);

struct Node{

  struct Node* next;
  struct Node* prev;
  int value;

};

struct Node* head;

main(){

  int i;
  int n;
  int tmpValue;
  char str[20];
  struct Node* node;

  head = (struct Node*)malloc(sizeof(struct Node));
  head->next = NULL;
  head->prev = NULL;
  head->value = 0;

  scanf("%d",&n);

  for(i=0; i<n; i++){
    scanf("%s",str);
    if(!strcmp(str,"insert")){
      scanf("%d",&tmpValue);
      insert(tmpValue);
    }else if(!strcmp(str,"deleteFirst")){
      deleteFirst();
    }else if(!strcmp(str,"deleteLast")){
      deleteLast();
    }else if(!strcmp(str,"delete")){
      scanf("%d",&tmpValue);
      delete(tmpValue);
    }
  }

  for(node=head->next; node != NULL; node=node->next){
    printf("%d",node->value);
    if(node->next!=NULL){
      printf(" ");
    }
  }
  printf("\n");

  return 0;

}

void insert(int _value){

  struct Node* newNode;
  struct Node* tmpNode;

  newNode = (struct Node*)malloc(sizeof(struct Node));

  tmpNode = head->next;
  if(tmpNode != NULL){
    tmpNode->prev = newNode;
  }
  head->next = newNode;
  newNode->next = tmpNode;
  newNode->prev = head;

  newNode->value = _value;

}

void delete(int _value){

  struct Node* node;
  struct Node* tmpNode;
  for(node=head->next; node != NULL; node=node->next){
    if(node->value == _value){
      tmpNode = node->prev;
      if(tmpNode != NULL){
	tmpNode->next = node->next;
      }
      if(node->next != NULL){
	node->next->prev = tmpNode;
      }
break;
    }
  }

}

void deleteFirst(){

  struct Node* node;
  //  struct Node* tmpNode;
  node=head->next;

  //  tmpNode = node->prev;
  //tmpNode = head;

  if(head != NULL){
    //tmpNode->next = node->next;
    head->next= node->next;
  }
  if(node->next != NULL){
    //   node->next->prev = tmpNode;
    node->next->prev = head;
  }
  free(node);

}

void deleteLast(){

  //struct Node* node;
  struct Node* tail;

  struct Node* tmpNode;

  //  for(node=head->next; node->next != NULL; node=node->next){}//node==tail
  for(tail=head->next; tail->next != NULL; tail=tail->next){}//node==tail

  /* tmpNode = tail->prev;

  if(tmpNode != NULL){
    tmpNode->next = NULL;
  }
  if(tail->next != NULL){
    tail->next->prev = tmpNode;
    }*/

 tail->prev->next=NULL;
  tail->prev=NULL;
  free(tail);

}