POJ.3692 Kindergarten

1.Problem
http://poj.org/problem?id=3692

2.Idea
Reverse the graph and take Bipartite Matching

3.Source

 #define MAX_V 1000  
 int V;  
 vector<int> G[MAX_V];  
 int match[MAX_V];  
 bool used[MAX_V];  
 bool g[500][500];  
 int GV, B, M;  
 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;  
 }  
 void solve(int t)  
 {  
      V = GV + B;  
      for (int i = 0; i <= V; i++) G[i].clear();  
      memset(used, 0, sizeof used);  
      for (int i = 0; i < 500; i++)  
           for (int j = 0; j < 500; j++)  
                g[i][j] = 1;  
      for (int i = 0; i < M; i++) {  
           int k, t;  
           scanf("%d%d", &t, &k);  
           t = t - 1;  
           k = GV + k - 1;  
           g[t][k] = g[k][t] = 0;  
      }  
      for (int i = 0; i < GV; i++) {  
           for (int j = GV; j < V; j++) {  
                if (g[i][j]) add_edge(i, j);  
           }  
      }  
      printf("Case %d: %d\n", t, GV + B - bipartite_matching());  
 }  
 int main()  
 {  
      int t = 1;  
      while (scanf("%d%d%d", &GV, &B, &M)>0) {  
           if (GV == 0) break;  
           solve(t);  
           t++;  
      }  
      return 0;  
 }