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 }