Codeforces round 1234(B2. Social Network (hard version))

Use map as visited not to get id's same messages every time

using deque as to consecutive sequence of k messages

///Bismillahir Rahmanir Rahim

///Author: Tanvir Ahmmad

///CSE,Islamic University,Bangladesh

#include<iostream>

#include<cstdio>

#include<algorithm>

#include<string>

#include<cstring>

#include<sstream>

#include<cmath>

#include<cstring>

#include<vector>

#include<queue>

#include<map>

#include<set>

#include<stack>

#include<vector>

#include<iterator>

#include <functional> ///sort(arr,arr+n,greater<int>()) for decrement of array

/*every external angle sum=360 degree

  angle find using polygon hand(n) ((n-2)*180)/n*/

///Floor[Log(b)  N] + 1 = the number of digits when any number is represented in base b

using namespace std;

typedef long long ll;

int main()

{

    ll n,k,num;

    map<ll,ll>mp;

    map<ll,ll>::iterator it;

    deque<ll>dq;

    cin>>n>>k;

    for(ll i=0; i<n; i++)

    {

        cin>>num;

        if(mp.find(num)==mp.end() || mp[num]==0)

        {

            mp[num]=1;

            if(dq.size()<k)

                dq.push_back(num);

            else

                mp[dq.front()]=0,dq.pop_front(),dq.push_back(num);

        }

    }

    cout<<dq.size()<<endl;

    while(dq.size())

        cout<<dq.back()<<" ",dq.pop_back();

    return 0;

}

///Alhamdulillah

Problem Link:https://codeforces.com/problemset/problem/1234/B2