【容斥+大数】SGU 476 Coach's Trouble

import java.util.*;
import java.math.*;

public class Solution {
    static int group[][] = new int[25][3];
    static int cnt[] = new int[25];
    static boolean vis[] = new boolean[3001];
    static int n, k, depth;

    static void Init() {
        for (int i = 0; i < 25; i++)
            cnt[i] = 0;
        for (int i = 0; i < 3001; i++)
            vis[i] = false;
    }

    static void DFS(int index, int now) {
        if (now == depth) {
            if (depth % 2 == 1)
                cnt[depth]++;
            else
                cnt[depth]--;
        } else {
            for (int i = index; i < k; i++) {
                if (vis[group[i][0]] == false && vis[group[i][1]] == false
                        && vis[group[i][2]] == false) {
                    vis[group[i][0]] = vis[group[i][1]] = vis[group[i][2]] = true;
                    DFS(i + 1, now + 1);
                    vis[group[i][0]] = vis[group[i][1]] = vis[group[i][2]] = false;
                }
            }
        }
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        BigInteger dp[] = new BigInteger[1001];
        BigInteger res;
        dp[0] = dp[1] = BigInteger.ONE;
        for (int i = 2; i < 1001; i++)
            dp[i] = dp[i - 1].multiply(BigInteger.valueOf(3 * i - 1))
                    .multiply(BigInteger.valueOf(3 * i - 2))
                    .divide(BigInteger.valueOf(2));
        while (in.hasNext()) {
            Init();
            n = in.nextInt();
            k = in.nextInt();
            for (int i = 0; i < k; i++) 
                for (int j = 0; j < 3; j++)
                    group[i][j] = in.nextInt();
            for (depth = 1; depth <= k; depth++)
                DFS(0, 0);
            res = BigInteger.ZERO;
            for (int i = 1; i <= k; i++) 
                if (cnt[i] != 0)
                    res = res.add(dp[n - i].multiply(BigInteger.valueOf(cnt[i])));
            System.out.println(dp[n].subtract(res));
        }
    }
}