C++ :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <algorithm>
#include <iostream>
#include <queue>
using namespace std;
int flag[10010];
int main()
{
    deque<int >q;
    int n,m,i,k;
    char str[10];
    memset(flag,0,sizeof(flag));
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%s",str);
        if(strcmp(str,"LIN")==0)
        {
            cin>>m;
            q.push_front(m);
        }
        else if(strcmp(str,"RIN")==0)
        {
            cin>>m;
            q.push_back(m);
        }
        else if(strcmp(str,"LOUT")==0)
        {
            if(!q.empty())
                q.pop_front();
            else
                flag[i]=1;
        }
        else if(strcmp(str,"ROUT")==0)
        {
            if(!q.empty())
                q.pop_back();
            else
                flag[i]=1;
        }

    }
        k=q.front();
        q.pop_front();
        cout<<k<<' ';
        while(!q.empty())
        {
            k=q.front();
            q.pop_front();
            cout<<k<<' ';
        }
        cout<<endl;
         for(i=1;i<=n;i++)
        {
            if(flag[i])
                cout<<i<<" "<<"ERROR"<<endl;
        }
}

Java :

import java.util.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int i, n = sc.nextInt(), t;
        String ac = null;
        boolean[] errors = new boolean[10001];
        Deque<Integer> dq = new ArrayDeque();
        for (i = 1; i <= n; i++) {
            ac = sc.next();
            errors[i] = false;
            if ("LIN".equals(ac)) {
                t = sc.nextInt();
                dq.addFirst(t);
            } else if ("RIN".equals(ac)) {
                t = sc.nextInt();
                dq.addLast(t);
            } else if ("LOUT".equals(ac)) {
                if (dq.size() > 0) dq.removeFirst();
                else {
                    errors[i] = true;
                }
            } else if ("ROUT".equals(ac)) {
                if (dq.size() > 0) dq.removeLast();
                else {
                    errors[i] = true;
                }
            }
        }
        while (dq.size() > 0) {
            System.out.print(dq.getFirst() + " ");
            dq.pop();
        }
        System.out.println();
        for (i = 1; i <= n; i++) {
            if (errors[i] == true) {
                System.out.println(i+" ERROR");
            }
        }
        sc.close();
    }
}