this part of code get accepted in PAT, but 6/11 on Acwing due to TLE.

#include <iostream>
#include <unordered_set>
#include <vector>
using namespace std;
const int N = 1e5 + 10;
int can_use[N * 2];
int guess_num[12][1010], person[12];
unordered_set<int> nouse_num;

int n, m;
int main()
{
    ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
    int x1, x2; cin >> x1 >> x2;
    can_use[abs(x1 - x2)] = 1;     //can_use[i] = 1 means this number is valid;
    nouse_num.emplace(x1), nouse_num.emplace(x2);   //record the existed nums
    cin >> n >> m;
    for (int i = 1; i <= n; i++ ) {
        for (int j = 1; j <= m; j++ ) cin >> guess_num[i][j];
    }

    int cnt = 0;        //num of person who is kicked out
    for (int r = 1; r <= m; r++ ) {
        for (int i = 1; i <= n; i++ ) {     //search from top to bottom to ensure order
            if (person[i]) continue;    //ignore the person who has been kicked out before
            int val = guess_num[i][r];
            if (can_use[val] and !nouse_num.count(val)) { //get right answer and not existed before
                for (int num: nouse_num) {
                    int new_num = abs(num - val);
                    can_use[new_num] = 1;
                }
                nouse_num.emplace(val);     //current val can't be used again

            }
            else {
                person[i] = 1;      //kick out this person
                if (cnt) cout << endl;
                cout << "Round #" << r << ": " << i << " is out.";
                cnt++ ; 
            }
        }
    }
    if (cnt) cout << endl;    
    if (cnt == n) {
        cout << "No winner.";
    }
    else {
        cout << "Winner(s):";
        for (int i = 1; i <= n; i++ ) {
            if (!person[i]) {
                cout << " " << i;
            }
        }
    }
    return 0;
}

delete can_use array, when checking value x, traversal nouse_num, suppose current value is t, then if (x + t) is in nouse_num, then we can make sure that x is correct because x + t - t = x

C++ (AC on ACWing)

#include <iostream>
#include <set>
using namespace std;
const int N = 1e5 + 10;
int guess_num[12][1010], person[12];
set<int> nouse_num;

int n, m;
int main()
{
    int x1, x2; scanf("%d%d", &x1, &x2);
    nouse_num.emplace(x1), nouse_num.emplace(x2);   //record the existed nums
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= n; i++ ) {
        for (int j = 1; j <= m; j++ ) scanf("%d", &guess_num[i][j]);
    }

    int cnt = 0;        //num of person who is kicked out
    for (int r = 1; r <= m; r++ ) {
        for (int i = 1; i <= n; i++ ) {     //search from top to bottom to ensure order
            if (!person[i]) {   //ignore the person who has been kicked out before
                int val = guess_num[i][r];
                bool valid =false;
                if (!nouse_num.count(val)){ //get right answer and not existed before
                    for (int num: nouse_num) {
                        int new_num = num + val;
                        if (nouse_num.count(new_num)) {
                            nouse_num.emplace(val);
                            valid = true;
                            break;
                        }
                        else {
                            valid = false;
                        }
                    }
                }    
                if (!valid) {
                    person[i] = 1;
                    if (cnt) cout << endl;
                    cout << "Round #" << r << ": " << i << " is out.";
                    cnt++;

                }//current val can't be used again
            }    
        }
    }
    if (cnt) puts("");    
    if (cnt == n) {
        printf("No winner.");
    }
    else {
        printf("Winner(s):");
        for (int i = 1; i <= n; i++ ) {
            if (!person[i]) {
                printf(" %d", i);
                //cout << " " << i;
            }
        }
    }
    return 0;
}

```