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。
1 #include<cstdio> 2 #include<iostream> 3 #include<cmath> 4 #include<algorithm> 5 #include<cstring> 6 #include<cstdlib> 7 #include<cctype> 8 #include<vector> 9 #include<stack> 10 #include<queue> 11 using namespace std; 12 #define enter puts("") 13 #define space putchar(' ') 14 #define Mem(a, x) memset(a, x, sizeof(a)) 15 #define rg register 16 typedef long long ll; 17 typedef double db; 18 const int INF = 0x3f3f3f3f; 19 const db eps = 1e-8; 20 const int maxn = 4e3 + 5; 21 inline ll read() 22 { 23 ll ans = 0; 24 char ch = getchar(), last = ' '; 25 while(!isdigit(ch)) {last = ch; ch = getchar();} 26 while(isdigit(ch)) {ans = ans * 10 + ch - '0'; ch = getchar();} 27 if(last == '-') ans = -ans; 28 return ans; 29 } 30 inline void write(ll x) 31 { 32 if(x < 0) x = -x, putchar('-'); 33 if(x >= 10) write(x / 10); 34 putchar(x % 10 + '0'); 35 } 36 37 int n, f, d, t; 38 39 struct Edge 40 { 41 int from, to, cap, flow; 42 }; 43 vector<Edge> edges; 44 vector<int> G[maxn]; 45 void addEdge(int from, int to) 46 { 47 edges.push_back((Edge){from, to, 1, 0}); 48 edges.push_back((Edge){to, from, 0, 0}); 49 int sz = edges.size(); 50 G[from].push_back(sz - 2); 51 G[to].push_back(sz - 1); 52 } 53 54 int dis[maxn]; 55 bool bfs() 56 { 57 Mem(dis, 0); dis[0] = 1; 58 queue<int> q; q.push(0); 59 while(!q.empty()) 60 { 61 int now = q.front(); q.pop(); 62 for(int i = 0; i < (int)G[now].size(); ++i) 63 { 64 Edge& e = edges[G[now][i]]; 65 if(!dis[e.to] && e.cap > e.flow) 66 { 67 dis[e.to] = dis[now] + 1; 68 q.push(e.to); 69 } 70 } 71 } 72 return dis[t]; 73 } 74 int cur[maxn]; 75 int dfs(int now, int res) 76 { 77 if(now == t || res == 0) return res; 78 int flow = 0, f; 79 for(int& i = cur[now]; i < (int)G[now].size(); ++i) 80 { 81 Edge& e = edges[G[now][i]]; 82 if(dis[e.to] == dis[now] + 1 && (f = dfs(e.to, min(res, e.cap - e.flow))) > 0) 83 { 84 e.flow += f; 85 edges[G[now][i] ^ 1].flow -= f; 86 flow += f; 87 res -= f; 88 if(res == 0) break; 89 } 90 } 91 return flow; 92 } 93 94 int maxflow() 95 { 96 int flow = 0; 97 while(bfs()) 98 { 99 Mem(cur, 0); 100 flow += dfs(0, INF); 101 } 102 return flow; 103 } 104 105 int main() 106 { 107 n = read(); f = read(); d = read(); 108 t = (n << 1) + f + d + 1; 109 for(int i = 1; i <= f; ++i) addEdge(0, i); 110 for(int i = 1; i <= d; ++i) addEdge((n << 1) + f + i, t); 111 for(int i = 1; i <= n; ++i) 112 { 113 addEdge(f + i, f + n + i); 114 int f1 = read(), d1 = read(); 115 for(int j = 1; j <= f1; ++j) 116 { 117 int x = read(); 118 addEdge(x, f + i); 119 } 120 for(int j = 1; j <= d1; ++j) 121 { 122 int x = read(); 123 addEdge(f + n + i, (n << 1) + f + x); 124 } 125 } 126 write(maxflow()); enter; 127 return 0; 128 }