poj3281 Dining

思路：

最大流。

实现：

#include <iostream>
#include <vector>
#include <cstring>
#include <queue>
using namespace std;

const int MAXV = 403, INF = 0x3f3f3f3f;
struct edge
{
    int to, cap, rev;
    edge(int t, int c, int r) { to = t; cap = c; rev = r; }
};
int level[MAXV];
int iter[MAXV];
vector<edge> G[MAXV];
int n, f, d;
void add_edge(int from, int to, int cap)
{
    edge e(to, cap, G[to].size());
    G[from].push_back(e);
    edge er(from, 0, G[from].size() - 1);
    G[to].push_back(er);
}
void bfs(int s)
{
    memset(level, -1, sizeof level);
    queue<int> q;
    level[s] = 0;
    q.push(s);
    while (!q.empty())
    {
        int v = q.front(); q.pop();
        for (int i = 0; i < G[v].size(); i++)
        {
            edge& e = G[v][i];
            if (e.cap > 0 && level[e.to] < 0)
            {
                level[e.to] = level[v] + 1;
                q.push(e.to);
            }
        }
    }
}
int dfs(int v, int t, int f)
{
    if (v == t) return f;
    for (int& i = iter[v]; i < G[v].size(); i++)
    {
        edge& e = G[v][i];
        if (e.cap > 0 && level[v] < level[e.to])
        {
            int d = dfs(e.to, t, min(f, e.cap));
            if (d > 0)
            {
                e.cap -= d;
                G[e.to][e.rev].cap += d;
                return d;
            }
        }
    }
    return 0;
}
int max_flow(int s, int t)
{
    int flow = 0;
    for (;;)
    {
        bfs(s);
        if (level[t] < 0) return flow;
        memset(iter, 0, sizeof iter);
        int f = 0;
        while ((f = dfs(s, t, INF)) > 0)
            flow += f;
    }
}

int main()
{
    cin >> n >> f >> d;
    for (int i = 1; i <= n; i++)
    {
        int t1, t2, x;
        cin >> t1 >> t2;
        for (int j = 1; j <= t1; j++)
        {
            cin >> x; add_edge(x, f + i, 1);
        }
        for (int j = 1; j <= t2; j++)
        {
            cin >> x; add_edge(f + n + i, f + 2 * n + x, 1);
        }
    }
    for (int i = 1; i <= f; i++) add_edge(0, i, 1);
    for (int i = 1; i <= d; i++) add_edge(f + 2 * n + i, f + 2 * n + d + 1, 1);
    for (int i = 1; i <= n; i++) add_edge(f + i, f + n + i, 1);
    cout << max_flow(0, f + 2 * n + d + 1) << endl;
    return 0;
}