题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1845
思路：匈牙利算法应用，900ms+险过。（好像直接n/2就行）
1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<vector> 6 using namespace std; 7 #define MAXN 5555 8 vector<int>map[MAXN]; 9 int n,m,ans; 10 bool mark[MAXN]; 11 int lx[MAXN],ly[MAXN]; 12 13 int dfs(int u){ 14 for(int i=0;i<map[u].size();i++){ 15 int v=map[u][i]; 16 if(!mark[v]){ 17 mark[v]=true; 18 if(ly[v]==-1||dfs(ly[v])){ 19 ly[v]=u; 20 lx[u]=v; 21 return 1; 22 } 23 } 24 } 25 return 0; 26 } 27 28 29 int main(){ 30 // freopen("1.txt","r",stdin); 31 int _case,u,v; 32 scanf("%d",&_case); 33 while(_case--){ 34 scanf("%d",&n);m=n*3/2;ans=0; 35 for(int i=1;i<=n;i++)map[i].clear(); 36 for(int i=1;i<=m;i++){ 37 scanf("%d%d",&u,&v); 38 map[u].push_back(v); 39 map[v].push_back(u); 40 } 41 memset(lx,-1,(n+2)*sizeof(lx[0])); 42 memset(ly,-1,(n+2)*sizeof(ly[0])); 43 for(int i=1;i<=n;i++){ 44 if(lx[i]==-1){ 45 memset(mark,false,(n+2)*sizeof(mark[0])); 46 ans+=dfs(i); 47 } 48 } 49 printf("%d\n",ans/2); 50 } 51 return 0; 52 }