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 <iostream>
#include <algorithm>
#include <deque>
#include <string>
#include <vector>
using namespace std;
typedef vector <string> svector;
typedef vector <int> ivector;
typedef deque <string> sdeque;

int split(svector &tokens, const string &text, char delim=' '){
	int start = 0, end = 0;
	while ((end = text.find(delim, start)) != string::npos){
		tokens.push_back(text.substr(start, end - start));
		start = end + 1;
	}
	tokens.push_back(text.substr(start));
	return 0;
}

int sdeque_out(sdeque &A){
    int n=A.size();
    for (int i=0; i<n; i++){
        cout << A[i];
        if (i!= n-1) cout<<" ";
        else cout<<endl;
    }
    return 0;
}

int main(void){
	int n;
	string text = "";
	svector strs;
	sdeque que;
	sdeque::iterator pos;
	
	cin >> n;
	getline(cin, text);

	for (int i=0; i<n; i++){
		getline(cin, text);
		strs.clear();
		split(strs, text);

		if (strs[0]== "insert")
			que.push_front(strs[1]);
		else if (strs[0] == "delete"){
			pos = find( que.begin(), que.end(), strs[1] );
			if (pos != que.end()) que.erase(pos);
		}else if (strs[0] == "deleteFirst")
			que.pop_front();
		else if (strs[0] == "deleteLast")
			que.pop_back();
	}

	sdeque_out(que);
	return 0;
}