https://www.luogu.com.cn/problem/U495933

#include <bits/stdc++.h>
using namespace std;
long long a[100002][2005];
int b[100005];
int c[100005];
int main() {
    // freopen("elements.in","r",stdin);
    // freopen("elements.out","w",stdout);
    int n;
    cin >> n;
    int t;
    cin >> t;
    for (int i = 1; i <= t; i++) {
        int l, le;
        cin >> l >> le;
        b[l]++;
        a[l][b[l]] = le;
    }
    for (int i = 1; i <= n; i++) {
        cout << b[i];
        for (int j = 1; j <= b[i]; j++) {
            c[j] = a[i][j];
        }
        sort(c, c + b[i] + 1);
        for (int j = 1; j <= b[i]; j++) {
            cout << ' ' << c[j];
        }
        cout << '\n';
    }

    return 0;
}