Title Link: https://vjudge.net/contest/252597#problem/C

1. Super memory, how to deal with it

#include<stdio.h>
#include<string>
#include<iostream>
#include<stack>
using namespace std;
typedef long long LL;
const int maxn = 300005;
stack<LL> nstack[maxn];
stack<LL> ss;
LL n, q,v,s;
int t,op;
void init()
{
    for (LL i = 0; i <= n; i++)
        while (!nstack[i].empty()) 
            nstack[i].pop();
}
int main()
{
    scanf("%d", &t);
    while (t--)
    {
        init();
        scanf("%lld%lld", &n, &q);
        while (q--)
        {
            scanf("%d", &op);
            if (op == 1)
            {
                scanf("%lld%lld", &s, &v);
                nstack[s].push(v);
            }
            else if (op == 2)
            {
                scanf("%lld", &s);
                if (nstack[s].size())
                {
                    LL tmp = nstack[s].top();
                    nstack[s].pop();
                    printf("%lld\n", tmp);
                }
                else puts("EMPTY");
            }
            else
            {
                while (!ss.empty())ss.pop();
                scanf("%lld%lld", &s, &v);
                while(!nstack[v].empty())
                {
                    ss.push(nstack[v].top());
                    nstack[v].pop();
                }
                while (!ss.empty())
                {
                    nstack[s].push(ss.top());
                    ss.pop();
                }
            }
        }
    }
    return 0;
}

Then I really can't optimize the memory. I'm dying to change some LL to int. although I know it's definitely not possible, I still want to hand in one. It's mle (but I know int can save 10 ^ 5)
Can't we use the stack of stl?
And then I went to see the underlying implementation

emmm I changed all the original code to int (int can also include 10 ^ 9 ah), and reported an error that never occurred: segment error
Is online God said to be a memory problem or compiler problem?

#include<string.h>
#include<stdio.h>
#include<string>
#include<iostream>
#include<stack>
using namespace std;
const int maxn = 1000005;
stack<int> nstack[maxn];
stack<int> ss;
int v, n, q, s;
int t, op;
void init()
{
    for (int i = 0; i <= n; i++)
        while (!nstack[i].empty()) nstack[i].pop();
}
int main()
{
    scanf("%d", &t);
    while (t--)
    {
        init();
        scanf("%d%d", &n, &q);
        while (q--)
        {
            scanf("%d", &op);
            if (op == 1)
            {
                scanf("%d%d", &s, &v);
                nstack[s].push(v);
            }
            else if (op == 2)
            {
                scanf("%d", &s);
                if (nstack[s].size())
                {
                    printf("%d\n", nstack[s].top());
                    nstack[s].pop();
                }
                else puts("EMPTY");
            }
            else
            {
                while (!ss.empty())ss.pop();
                scanf("%d%d", &s, &v);
                while (!nstack[v].empty())
                {
                    ss.push(nstack[v].top());
                    nstack[v].pop();
                }
                while (!ss.empty())
                {
                    nstack[s].push(ss.top());
                    ss.pop();
                }
            }
        }
    }
    return 0;
}

I tried vector, still mle

#include<stdio.h>
#include<string>
#include<iostream>
#include<vector>
using namespace std;
const int maxn = 1000005;
vector<int> nstack[maxn];
int n, q, s,v;
int t, op;
void init()
{
    for (int i = 0; i <= n; i++)
        nstack[i].clear();
}
int main()
{
    scanf("%d", &t);
    while (t--)
    {
        init();
        scanf("%d%d", &n, &q);
        while (q--)
        {
            scanf("%d", &op);
            if (op == 1)
            {
                scanf("%d%d", &s, &v);
                nstack[s].push_back(v);
            }
            else if (op == 2)
            {
                scanf("%d", &s);
                if (nstack[s].size())
                {
                    printf("%d\n", nstack[s][nstack[s].size() - 1]);
                    nstack[s].pop_back();
                }
                else puts("EMPTY");
            }
            else
            {
                scanf("%d%d", &s, &v);
                nstack[s].insert(nstack[s].end(),nstack[v].begin(), nstack[v].end());
                nstack[v].clear();
            }
        }
    }
    return 0;
}

I'll change the list. It's over
(there's a magic function called splice)

#include<stdio.h>
#include<string>
#include<iostream>
#include<list>
using namespace std;
const int maxn = 1000005;
list<int> nstack[maxn];
int v, n, q, s;
int t, op;
void init()
{
    for (int i = 0; i <= n; i++)
        nstack[i].clear();
}
int main()
{
    scanf("%d", &t);
    while (t--)
    {
        init();
        scanf("%d%d", &n, &q);
        while (q--)
        {
            scanf("%d", &op);
            if (op == 1)
            {
                scanf("%d%d", &s, &v);
                nstack[s].push_back(v);
            }
            else if (op == 2)
            {
                scanf("%d", &s);
                if (!nstack[s].empty())
                {
                    printf("%d\n", nstack[s].back());
                    nstack[s].pop_back();
                }
                else puts("EMPTY");
            }
            else
            {
                scanf("%d%d", &s, &v);
                nstack[s].splice(nstack[s].end(), nstack[v]);
                //I've tried it. I'll timeout if I don't use the built-in function
                /*while (!nstack[v].empty())
                {
                    nstack[s].push_back(nstack[v].front());
                    nstack[v].pop_front();
                }*/
            }
        }
    }
    return 0;
}

Explanation from the great gods
Why can't I use stack

Forget to add the way that the big bulls use arrays: put all the numbers in an array a, and record the numbers of the top, bottom and top of the stack in array a with three arrays top, bottom and next