Codeforces Round #590 (Div. 3), problem: (B2) Social Network (hard version)

#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")

#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define pii pair<int,int>
#define pli pair<long long int,int>
#define pbi pair<bool,int>
#define pob pop_back
#define all(a) a.begin(),a.end()
#define fio ios_base::sync_with_stdio(false); cin.tie(0);cout.tie(0);
#define i64 long long int
#define mem(x,y) memset(x,y,sizeof(x))
#define fill(arr,b) fill(arr, arr+sizeof(arr)/sizeof(arr[0]), b)
#define maxarr(n,arr,m) m =-1e9;for(int i=0;i<n;i++)if(arr[i]>m) m=arr[i];
#define read freopen("input.txt","r",stdin);

const double pi = acos(-1.0);
const int maxn = (i64)1e9+7;
i64 arr[200005];
map<i64,bool>mp;
int main()
{
    //read;
    int n,k,a,f=0,l=0;
    scanf("%d%d",&n,&k);
    for(int i=0;i<n;i++)
    {
        scanf("%d",&a);
        if(mp[a]==1) continue;
        if(f-l==k)
        {
            mp[arr[l]]=0;
            l++;
            arr[f++]=a;
            mp[a]=1;
            continue;
        }
        arr[f++]=a;
        mp[a]=1;
    }
    printf("%d\n",f-l);
    for(int i=f-1;i>=l;i--) printf("%d ",arr[i]);

    return 0;
}