HDU——T The King’s Problem

  1 #include <cstring>
  2 #include <cstdio>
  3 
  4 #define min(a,b) (a<b?a:b)
  5 #define max(a,b) (a>b?a:b)
  6 const int N(5000+115);
  7 const int M(100000+5);
  8 int hed[N],sumedge,had[N];
  9 struct Edge
 10 {
 11     int v,next;
 12     Edge(int v=0,int next=0):v(v),next(next){}
 13 }edge[M],e[M];
 14 inline void ins(int u,int v,int *head,Edge *edge)
 15 {
 16     edge[++sumedge]=Edge(v,head[u]);
 17     head[u]=sumedge;
 18 }
 19 
 20 int tim,dfn[N],low[N];
 21 int top,instack[N],Stack[N];
 22 int sumcol,col[N],rd[N],cd[N];
 23 void DFS(int u)
 24 {
 25     low[u]=dfn[u]=++tim;
 26     Stack[++top]=u; instack[u]=1;
 27     for(int v,i=hed[u];i;i=edge[i].next)
 28     {
 29         v=edge[i].v;
 30         if(!dfn[v]) DFS(v), low[u]=min(low[u],low[v]);
 31         else if(instack[v]) low[u]=min(low[u],dfn[v]);
 32     }
 33     if(low[u]==dfn[u])
 34     {
 35         col[u]=++sumcol;
 36         for(;u!=Stack[top];top--)
 37         {
 38             col[Stack[top]]=sumcol;
 39             instack[Stack[top]]=0;
 40         }
 41         instack[u]=0; top--;
 42     }
 43 }
 44 
 45 int sumvis,vis[N],match[N];
 46 bool find(int u)
 47 {
 48     for(int v,i=had[u];i;i=e[i].next)
 49     {
 50         v=e[i].v;
 51         if(vis[v]==sumvis) continue;
 52         vis[v]=sumvis;
 53         if(!match[v]||find(match[v]))
 54         {
 55             match[v]=u;
 56             return true;
 57         }
 58     }
 59     return false;
 60 }
 61 
 62 inline void init()
 63 {
 64     tim=top=sumedge=sumcol=sumvis=0;
 65     memset(e,0,sizeof(e));
 66     memset(vis,0,sizeof(vis));
 67     memset(col,0,sizeof(col));
 68     memset(dfn,0,sizeof(dfn));
 69     memset(low,0,sizeof(low));
 70     memset(hed,0,sizeof(hed));
 71     memset(had,0,sizeof(had));
 72     memset(edge,0,sizeof(edge));
 73     memset(Stack,0,sizeof(Stack));
 74     memset(match,0,sizeof(match));
 75     memset(instack,0,sizeof(instack));
 76 }
 77 inline void read(int &x)
 78 {
 79     x=0; register char ch=getchar();
 80     for(;ch>‘9‘||ch<‘0‘;) ch=getchar();
 81     for(;ch>=‘0‘&&ch<=‘9‘;ch=getchar()) x=x*10+ch-‘0‘;
 82 }
 83 
 84 int main()
 85 {
 86     int t; read(t);
 87     for(int n,m;t--;init())
 88     {
 89         read(n),read(m);
 90         for(int u,v;m--;)
 91             read(u),read(v),ins(u,v,hed,edge);
 92         for(int i=1;i<=n;i++)
 93             if(!dfn[i]) DFS(i);
 94         for(int u=1;u<=n;u++)
 95             for(int v,i=hed[u];i;i=edge[i].next)
 96             {
 97                 v=edge[i].v;
 98                 if(col[u]!=col[v]) ins(col[u],col[v],had,e);
 99             }
100         int ans=0;
101         for(int i=1;i<=sumcol;i++)
102         {
103             sumvis++;
104             if(find(i)) ans++;
105         }
106         printf("%d\n",sumcol-ans);
107     }
108     return 0;
109 }