#include<iostream>
#include<unordered_set>
#include<vector>
using namespace std;
int SetInter(int arr1[],int len1,int arr2[],int len2,int res[]) {
    unordered_set<int> seen;
    vector<int> unique_arr1;
    for(int i=0; i<len1; ++i) {
        if(seen.find(arr1[i])==seen.end()) {
            seen.insert(arr1[i]);
            unique_arr1.push_back(arr1[i]);
        }
    }
    unordered_set<int> set_arr2;
    for(int i=0; i<len2; ++i)set_arr2.insert(arr2[i]);
    int count=0;
    for(int num:unique_arr1) {
        if(set_arr2.count(num))res[count++]=num;
    }
    return count;
}
int main() {
    const int MAX_SIZE=10000;
    int a1[MAX_SIZE],a2[MAX_SIZE],a3[MAX_SIZE],res[MAX_SIZE];
    int n1,n2,n3;
    cin>>n1>>n2>>n3;
    for(int i=0; i<n1; ++i)cin>>a1[i];
    for(int i=0; i<n2; ++i)cin>>a2[i];
    for(int i=0; i<n3; ++i)cin>>a3[i];
    int len1=SetInter(a1,n1,a2,n2,res);
    for(int i=0; i<len1; ++i) {
        if(i>0)cout<<" ";
        cout<<res[i];
    }
    cout<<endl;
    int len2=SetInter(a1,n1,a3,n3,res);
    for(int i=0; i<len2; ++i) {
        if(i>0)cout<<" ";
        cout<<res[i];
    }
    cout<<endl;
    return 0;
}

what can I say?
Manba out!

#include <bits/stdc++.h>
using namespace std;
const int N=10005;
int a[N],b[N],c[N],n1,n2,n3;
int main()
{
    cin>>n1>>n2>>n3;
    for(int i=1;i<=n1;i++)
    {
        cin>>a[i];
    }
    for(int i=1;i<=n2;i++)
    {
        cin>>b[i];
    }
    for(int i=1;i<=n3;i++)
    {
        cin>>c[i];
    }
    for(int i=1;i<=n1;i++)
    {
        for(int j=1;j<=n2;j++)
        {
            if(a[i]==b[j]) cout<<a[i]<<' ';
        }
    }
    cout<<endl;
    for(int i=1;i<=n1;i++)
    {
        for(int j=1;j<=n3;j++)
        {
            if(a[i]==c[j]) cout<<a[i]<<' ';
        }
    }
    return 0;
}