Submission #7922934

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Source Code Expand

#include <iostream>
#include <vector>

using namespace std;
struct UnionFind {
	vector<int> par;

	UnionFind(int N) : par(N) {
		for(int i = 0; i < N; i++) par[i] = i;
	}

	int root(int x) {
		if(par[x] == x) return x;
			//ここで併合処理も行なっている
		return par[x] = root(par[x]);
	}

	void unite(int x, int y) {
		int rx = root(x);
		int ry = root(y);
		if(rx == ry) return;
		par[rx] = ry;
	}

	bool same(int x, int y) {
		int rx = root(x);
		int ry = root(y);
		return rx == ry;
	}

};


int main() {
	int N;
	cin >> N;
	UnionFind a(N);
	int M;
	cin >> M;
	vector<vector<bool> > L(N, vector<bool>(M, false));

	for(int i = 0; i < N; i++) {
		int ki;
		cin >> ki;
		for(int j = 0; j < ki; j++) {
			int x;
			cin >> x;
			L[i][x - 1] = true;
		}
	}

	for(int l = 0; l < M; l++) {
		int first_hit = -1;
		for(int i = 0; i < N; i++) {
			if(L[i][l] == true) {
				if(first_hit == -1) first_hit = i;
				else a.unite(first_hit, i);
			}
		}
	}

	for(int i = 0; i < N; i++) {
		for(int j = i + 1; j < N; j++) {
			if(a.same(i, j) == false) {
				cout << "NO" << endl;
				return 0;
			}
		}
	}
	cout << "YES" << endl;
}

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