题目链接

题意：


题解：





/*
    Author : zzugzx
    Lang : C++
    Blog : blog.csdn.net/qq_43756519
*/
#include<bits/stdc++.h>
using namespace std;

#define fi first
#define se second
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(), (x).end()
#define endl '\n'
#define SZ(x) (int)x.size()
#define mem(a, b) memset(a, b, sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int mod = 1e9 + 7;
//const int mod = 998244353;

const double eps = 1e-6;
const double pi = acos(-1.0);
const int maxn = 1e6 + 10;
const int N = 1e2 + 5;
const ll inf = 0x3f3f3f3f;
const int dir[][2]={{0, 1}, {1, 0}, {0, -1}, {-1, 0}, {1, 1}, {1, -1}, {-1, 1}, {-1, -1}};
int n, k;
int cnt[maxn];
bool ok() {
    for (int i = 1; i <= k; i++)
        if (!cnt[i]) return 0;
    return 1;
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
//  freopen("in.txt", "r", stdin);
//  freopen("out.txt", "w", stdout);
    cin >> n >> k;
    vector<pii> v;
    for (int i = 1; i <= k; i++) {
        int t;
        cin >> t;
        while (t--) {
            int x;
            cin >> x;
            v.pb(mp(x, i));
        }
    }
    sort(all(v));
    int ans = inf, l = 0;
    for (int r = 0; r < n; r++) {
        cnt[v[r].se]++;
        while (ok()) ans = min(ans, v[r].fi - v[l].fi), cnt[v[l++].se]--;
    }
    cout << ans << endl;
    return 0;
}