[USACO07OPEN]吃饭Dining

嘟嘟嘟

这应该是网络流入门题之一了，跟教辅的组成这道题很像。

把每一只牛看成书，然后对牛拆点，因为每一只牛只要一份，食物和饮料分别看成练习册和答案。

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<algorithm>
 #include<cstring>
 #include<cstdlib>
 #include<cctype>
 #include<vector>
 #include<stack>
 #include<queue>
 using namespace std;
 #define enter puts("")
 #define space putchar(' ')
 #define Mem(a, x) memset(a, x, sizeof(a))
 #define rg register
 typedef long long ll;
 typedef double db;
 const int INF = 0x3f3f3f3f;
 const db eps = 1e-;
 const int maxn = 4e3 + ;
 inline ll read()
 {
     ll ans = ;
     char ch = getchar(), last = ' ';
     while(!isdigit(ch)) {last = ch; ch = getchar();}
     while(isdigit(ch)) {ans = ans *  + ch - ''; ch = getchar();}
     if(last == '-') ans = -ans;
     return ans;
 }
 inline void write(ll x)
 {
     if(x < ) x = -x, putchar('-');
     if(x >= ) write(x / );
     putchar(x %  + '');
 }

 int n, f, d, t;

 struct Edge
 {
     int from, to, cap, flow;
 };
 vector<Edge> edges;
 vector<int> G[maxn];
 void addEdge(int from, int to)
 {
     edges.push_back((Edge){from, to, , });
     edges.push_back((Edge){to, from, , });
     int sz = edges.size();
     G[from].push_back(sz - );
     G[to].push_back(sz - );
 }

 int dis[maxn];
 bool bfs()
 {
     Mem(dis, ); dis[] = ;
     queue<int> q; q.push();
     while(!q.empty())
     {
         int now = q.front(); q.pop();
         for(int i = ; i < (int)G[now].size(); ++i)
         {
             Edge& e = edges[G[now][i]];
             if(!dis[e.to] && e.cap > e.flow)
             {
                 dis[e.to] = dis[now] + ;
                 q.push(e.to);
             }
         }
     }
     return dis[t];
 }
 int cur[maxn];
 int dfs(int now, int res)
 {
     if(now == t || res == ) return res;
     int flow = , f;
     for(int& i = cur[now]; i < (int)G[now].size(); ++i)
     {
         Edge& e = edges[G[now][i]];
         if(dis[e.to] == dis[now] +  && (f = dfs(e.to, min(res, e.cap - e.flow))) > )
         {
             e.flow += f;
             edges[G[now][i] ^ ].flow -= f;
             flow += f;
             res -= f;
             if(res == ) break;
         }
     }
     return flow;
 }

 int maxflow()
 {
     int flow = ;
     while(bfs())
     {
         Mem(cur, );
         flow += dfs(, INF);
     }
     return flow;
 }

 int main()
 {
     n = read(); f = read(); d = read();
     t = (n << ) + f + d + ;
     for(int i = ; i <= f; ++i) addEdge(, i);
     for(int i = ; i <= d; ++i) addEdge((n << ) + f + i, t);
     for(int i = ; i <= n; ++i)
     {
         addEdge(f + i, f + n + i);
         int f1 = read(), d1 = read();
         for(int j = ; j <= f1; ++j)
         {
             int x = read();
             addEdge(x, f + i);
         }
         for(int j = ; j <= d1; ++j)
         {
             int x = read();
             addEdge(f + n + i, (n << ) + f + x);
         }
     }
     write(maxflow()); enter;
     return ;
 }