POJ.3041 Asteroids

1.Problem
http://poj.org/problem?id=3041

2.Idea
Bipartite Matching

3.Source

 #define MAX_V 1000  
 int V;  
 vector<int> G[MAX_V];  
 int match[MAX_V];  
 bool used[MAX_V];  
 void add_edge(int u, int v)  
 {  
      G[u].push_back(v);  
      G[v].push_back(u);  
 }  
 bool dfs(int v)  
 {  
      used[v] = true;  
      for (int i = 0; i < G[v].size(); i++) {  
           int u = G[v][i], w = match[u];  
           if (w < 0 || !used[w] && dfs(w)) {  
                match[v] = u;  
                match[u] = v;  
                return true;  
           }  
      }  
      return false;  
 }  
 int bipartite_matching()  
 {  
      int res = 0;  
      memset(match, -1, sizeof match);  
      for (int v = 0; v < V; v++) {  
           if (match[v] < 0) {  
                memset(used, 0, sizeof used);  
                if (dfs(v)) {  
                     res++;  
                }  
           }  
      }  
      return res;  
 }  
 #define MAX_K 10000  
 int N, K;  
 int R[MAX_K], C[MAX_K];  
 void solve()  
 {  
      V = N * 2;  
      for (int i = 0; i < K; i++) {  
           add_edge(R[i] - 1, N + C[i] - 1);  
      }  
      printf("%d\n", bipartite_matching());  
 }  
 int main()  
 {  
      scanf("%d%d", &N, &K);  
      for (int i = 0; i < K; i++) {  
           scanf("%d%d", &R[i], &C[i]);  
      }  
      solve();  
      return 0;  
 }