Submission #1798558

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Source Code Expand

#include<iostream>
#include<vector>
#include<bitset>

using namespace std;
typedef long long ll;

int N, M;
ll dp[1 << 16];
int in[16];
vector<vector<int>> e;

ll memo(int bit, int nokori[16]) {
	ll res = 0;

	if (bit == (1 << N) - 1)return dp[bit] = 1;
	if (dp[bit] != 0)return dp[bit];
	for (int i = 0; i < N; i++) {
		if (nokori[i] == 0 && !(bit & (1 << i))) {
			vector<int> delta;

			for (int j = 0; j < e[i].size(); j++) {
				if (nokori[e[i][j]] != 0)delta.push_back(j);
			}

			for (int j = 0; j < delta.size(); j++) {
				nokori[e[i][delta[j]]]--;
			}

			res += memo(bit | (1 << i), nokori);

			for (int j = 0; j < delta.size(); j++) {
				nokori[e[i][delta[j]]]++;
			}
		}
	}
	return dp[bit] = res;
}

int main() {
	cin >> N >> M;
	e.resize(N);
	for (int i = 0; i < M; i++) {
		int a, b;
		cin >> a >> b;
		a--, b--;
		e[a].push_back(b);
		in[b]++;
	}
	cout << memo(0, in) << endl;
	return 0;
}

Submission Info

Judge Result