洛谷 P2891 [USACO07OPEN]吃饭Dining

裸的最大流。

#include <cstdio>
#include <cstring>
#include <queue>

const int MAXN = 4e3 + 19, MAXM = 4e6 + 19;

struct Edge{
	int to, next, c;
}edge[MAXM];

int cnt = -1, head[MAXN];

inline void add(int from, int to, int c){
	edge[++cnt].to = to;
	edge[cnt].c = c;
	edge[cnt].next = head[from];
	head[from] = cnt;
}

int n, f, d;

int dep[MAXN];

int bfs(void){
	std::queue<int>q; q.push(0);
	std::memset(dep, 0, sizeof dep); dep[0] = 1;
	while(!q.empty()){
		int node = q.front(); q.pop();
		for(int i = head[node]; i != -1; i = edge[i].next)
			if(!dep[edge[i].to] && edge[i].c)
				dep[edge[i].to] = dep[node] + 1, q.push(edge[i].to);
	}
	return dep[f + n + n + d + 1];
}

inline int min(const int& a, const int& b){
	return a < b ? a : b;
}

int dfs(int node, int flow){
	if(node == f + n + n + d + 1 || !flow)
		return flow;
	int stream = 0, f;
	for(int i = head[node]; i != -1; i = edge[i].next)
		if(dep[edge[i].to] == dep[node] + 1 && (f = dfs(edge[i].to, min(flow, edge[i].c)))){
			flow -= f, stream += f;
			edge[i].c -= f, edge[i ^ 1].c += f;
			if(!flow)
				break;
		}
	return stream;
}

int dinic(void){
	int flow = 0;
	while(bfs())
		flow += dfs(0, 0x3f3f3f3f);
	return flow;
}

int main(){
	std::memset(head, -1, sizeof head);
	std::scanf("%d%d%d", &n, &f, &d);
	for(int i = 1; i <= f; ++i)
		add(0, i, 1), add(i, 0, 0);
	for(int i = f + 1; i <= f + n; ++i)
		add(i, i + n, 1), add(i + n, i, 0);
	for(int i = f + n + n + 1; i <= f + n + n + d; ++i)
		add(i, f + n + n + d + 1, 1), add(f + n + n + d + 1, i, 0);
	for(int a, b, i = 1; i <= n; ++i){
		int l;
		std::scanf("%d%d", &a, &b);
		while(a--){
			std::scanf("%d", &l);
			add(l, f + i, 1), add(f + i, l, 0);
		}
		while(b--){
			std::scanf("%d", &l);
			add(f + n + i, f + n + n + l, 1), add(f + n + n + l, f + n + i, 0);
		}
	}
	std::printf("%d\n", dinic());
	return 0;
}