1802C - The Very Beautiful Blanket - CodeForces Solution

#include<bits/stdc++.h>
#define int long long
using namespace std;
using LL = long long;
#define rd dist(rnd)

signed main() {

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);
    mt19937_64 rnd(random_device{}());
    uniform_int_distribution<LL> dist(0, LLONG_MAX);
    

    int T;
    cin >> T;
    while(T--){
        int n, m;
    cin >> n >> m;
    vector<vector<LL> > a(n, vector<LL>(m));
    while (1) {
        set<int> se;
        for (int i = 0;i < n;i++)
            a[i][0] = rd;
        for (int i = 0;i < m;i++)
            a[0][i] = rd;
        int tar = rd;
        for (int i = 1;i < n;i++)
            for (int j = 1;j < m;j++)
                a[i][j] = tar ^ a[i - 1][j - 1] ^ a[i][j - 1] ^ a[i - 1][j];

        for (int i = 0;i < n;i++)
            for (int j = 0;j < m;j++)
                se.insert(a[i][j]);
        if (se.size() == n * m){
                cout << n * m << '\n';
                for(int i = 0; i < n; i++){
                    for(int j = 0; j < m; j++){
                        cout << a[i][j] << " \n"[j == m - 1];
                    }
                }
                break;
            }
    }
    }

}