hdu2063 过山车
1 #include <bits/stdc++.h> 2 using namespace std; 3 const int maxn = 2005, inf = 0x3f3f3f; 4 struct Edge { 5 int from, to, cap, flow; 6 }; 7 8 struct Dinic { 9 int n, m, s, t; 10 vector<Edge> edges; 11 vector<int> G[maxn]; 12 bool vis[maxn]; 13 int d[maxn]; 14 int cur[maxn]; 15 16 void init(int n) { 17 this->n = n; 18 for (int i = 1; i <= n; ++i) { 19 G[i].clear(); 20 } 21 edges.clear(); 22 } 23 void AddEdge(int from, int to, int cap) { 24 edges.push_back((Edge){from, to, cap, 0}); 25 edges.push_back((Edge){to, from, 0, 0}); 26 m = edges.size(); 27 G[from].push_back(m-2); 28 G[to].push_back(m-1); 29 } 30 bool bfs() { 31 memset(vis, 0, sizeof(vis)); 32 queue<int> que; 33 que.push(s); 34 d[s] = 0; 35 vis[s] = true; 36 while (!que.empty()) { 37 int x = que.front(); que.pop(); 38 for (int i = 0; i < G[x].size(); ++i) { 39 Edge& e = edges[G[x][i]]; 40 if (!vis[e.to] && e.cap > e.flow) { 41 vis[e.to] = true; 42 d[e.to] = d[x] + 1; 43 que.push(e.to); 44 } 45 } 46 } 47 return vis[t]; 48 } 49 int dfs(int x, int a) { 50 if (x == t || a == 0) return a; 51 int flow = 0, f; 52 for (int& i = cur[x]; i < G[x].size(); ++i) { 53 Edge& e = edges[G[x][i]]; 54 if (d[x] + 1 == d[e.to] && (f = dfs(e.to, min(a, e.cap-e.flow))) > 0) { 55 e.flow += f; 56 edges[G[x][i]^1].flow -= f; 57 flow += f; 58 a -= f; 59 if (a == 0) break; 60 } 61 } 62 return flow; 63 } 64 int maxflow(int s, int t) { 65 this->s = s; this->t = t; 66 int flow = 0; 67 while (bfs()) { 68 memset(cur,0,sizeof(cur)); 69 flow += dfs(s,inf); 70 } 71 return flow; 72 } 73 }dinic; 74 int main() { 75 int e; 76 while (~scanf("%d",&e) && e) { 77 int n, m; scanf("%d%d",&n,&m); 78 dinic.init(n+m+2); 79 int s = n+m+1, t = n+m+2; 80 for (int i = 1; i <= n; ++i) { 81 dinic.AddEdge(s,i,1); 82 } 83 for (int i = 1; i <= m; ++i) { 84 dinic.AddEdge(i+n,t,1); 85 } 86 for (int i = 1; i <= e; ++i) { 87 int u, v; scanf("%d%d",&u,&v); 88 dinic.AddEdge(u,v+n,1); 89 } 90 int ans = dinic.maxflow(s,t); 91 printf("%d\n",ans); 92 } 93 return 0; 94 }
