제출 #1039387

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1039387		ef10	Amusement Park (CEOI19_amusementpark)	C++17	0 / 100	0 ms	440 KiB

amusementpark

// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;

#define LL long long
#define MODULE 998244353

int N,M;
vector<int> adj[20];
LL dp[1<<18][20];

LL exp(LL a, LL b) {
		if (a==0) return 0;
        if (b == 0) return 1;
        LL ret = exp(a, b/2);
        ret = ret * ret;
        ret %= MODULE;
        if (b % 2) {
                ret *= a;
                ret %= MODULE;
        }
        return ret;
}

LL inv(LL x) {
        return exp(x, MODULE-2);
}

int main() {
	cin >> N >> M;
	for (int i = 0; i < M; i++) {
		int a,b; cin >> a >> b; a--;b--;
		adj[a].push_back(b);
		adj[b].push_back(a);
	}
	for (int i = 0; i < N; i++) {
		dp[1<<i][i]=1;
	}
	for (int i = 0; i < (1<<N); i++) {
		for (int j = 0; j < N; j++) {
			if (dp[i][j] == 0) continue;
			for (auto n : adj[j]) {
				if (i & (1<<n)) continue;
				dp[i | (1<<n)][n] += dp[i][j];
				dp[i | (1<<n)][n] %= MODULE;
			}
		}
	}
	LL res = 0;
	for (int i = 0; i < N; i++) {
		res += dp[(1<<N)-1][i];
		res %= MODULE;
	}
	//cout << res << endl;
	res *= M;
	res %= MODULE;
	res *= inv(2);
	res %= MODULE;
	cout << res << endl;
}

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