[luoguP3068] [USACO13JAN]派对邀请函Party Invitations（stl大乱交）

传送门

 

记录每一个编号在那些组中，可以用vector，这里选择链式前向星。

每一组用set

将被邀请的放到queue中

 

#include <set>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#define N 1000001

using namespace std;

int n, g, cnt, ans;
int head[N], to[N], next[N];
queue <int> q;
set <int> s[N];
set <int> :: iterator it;
bool b[N];

inline int read()
{
	int x = 0, f = 1;
	char ch = getchar();
	for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
	return x * f;
}

inline void add(int x, int y)
{
	to[cnt] = y;
	next[cnt] = head[x];
	head[x] = cnt++;
}

int main()
{
	int i, j, k, x, u, v;
	n = read();
	g = read();
	memset(head, -1, sizeof(head));
	for(i = 1; i <= g; i++)
	{
		k = read();
		for(j = 1; j <= k; j++)
		{
			x = read();
			s[i].insert(x);
			add(x, i);
		}
	}
	q.push(1);
	while(!q.empty())
	{
		ans++;
		u = q.front();
		q.pop();
		for(i = head[u]; i ^ -1; i = next[i])
		{
			v = to[i];
			s[v].erase(u);
			it = s[v].begin();
			if(s[v].size() == 1 && !b[*it])
			{
				b[*it] = 1;
				q.push(*it);
			}
		}
	}
	printf("%d\n", ans);
	return 0;
}