POJ 2186 Popular Cows(Tarjan)

看着DISCUSS各种改。。Tarjan每个点属于那个连通块，枚举度数，统计出度。如果出度为0的有一个，这个块的个数就是结果。出度为0的大于1，则没有。

  1 #include <iostream>
  2 #include <cstring>
  3 #include <cstdio>
  4 #include <cstdlib>
  5 using namespace std;
  6 #define N 10001
  7 #define M 50001
  8 struct node
  9 {
 10     int u,v,next;
 11 } edge[M+10];
 12 int t,top,scnt;
 13 int DFN[N+1],Low[N+1],Belong[N+1],stack[N+1],first[N+1],count[N+1];
 14 int in[N+1],flag[N+1];
 15 int quex[M+1],quey[M+1];
 16 void CL()
 17 {
 18     t = 0;
 19     t = scnt = top = 0;
 20     memset(first,-1,sizeof(first));
 21     memset(DFN,0,sizeof(DFN));
 22     memset(flag,0,sizeof(flag));
 23     memset(count,0,sizeof(count));
 24 }
 25 void add(int u,int v)
 26 {
 27     edge[t].u = u;
 28     edge[t].v = v;
 29     edge[t].next = first[u];
 30     first[u] = t ++;
 31 }
 32 void Tarjan(int u)
 33 {
 34     int v,i;
 35     DFN[u] = Low[u] = ++ t;
 36     in[u] = 1;
 37     stack[top++] = u;
 38     for(i = first[u]; i != -1; i = edge[i].next)
 39     {
 40         v = edge[i].v;
 41         if(!DFN[v])
 42         {
 43             Tarjan(v);
 44             if(Low[u] > Low[v])
 45             {
 46                 Low[u] = Low[v];
 47             }
 48         }
 49         else if(in[v] && Low[u] > DFN[v])
 50         {
 51             Low[u] = DFN[v];
 52         }
 53     }
 54     if(DFN[u] == Low[u])
 55     {
 56         scnt ++;
 57         do
 58         {
 59             v = stack[--top];
 60             in[v] = 0;
 61             Belong[v] = scnt;
 62             count[scnt] ++;
 63         }
 64         while(u != v);
 65     }
 66 }
 67 int main()
 68 {
 69     int n,m,sv,ev,num,key,i;
 70     while(scanf("%d%d",&n,&m)!=EOF)
 71     {
 72         CL();
 73         for(i = 1; i <= m; i ++)
 74         {
 75             scanf("%d%d",&sv,&ev);
 76             quex[i] = sv;
 77             quey[i] = ev;
 78             add(sv,ev);
 79         }
 80         t = 0;
 81         for(i = 1; i <= n; i ++)
 82         {
 83             if(!DFN[i])
 84                 Tarjan(i);
 85         }
 86         for(i = 1; i <= m; i ++)
 87         {
 88             if(Belong[quex[i]] != Belong[quey[i]])
 89             {
 90                 flag[Belong[quex[i]]] ++;
 91             }
 92         }
 93         num = 0;
 94         for(i = 1; i <= scnt; i ++)
 95         {
 96             if(flag[i] == 0)
 97             {
 98                 num ++;
 99                 key = i;
100             }
101         }
102         if(num == 1)
103             printf("%d\n",count[key]);
104         else
105             printf("0\n");
106     }
107     return 0;
108 }

 

posted @ 2013-04-01 21:06  Naix_x  阅读(141)  评论(0)    收藏  举报