POJ2186 Popular Cows

  1 //It is made by jump~
  2 #include <iostream>
  3 #include <cstdlib>
  4 #include <cstring>
  5 #include <cstdio>
  6 #include <cmath>
  7 #include <algorithm>
  8 #include <ctime>
  9 #include <vector>
 10 #include <queue>
 11 #include <map>
 12 #ifdef WIN32   
 13 #define OT "%I64d"
 14 #else
 15 #define OT "%lld"
 16 #endif
 17 using namespace std;
 18 typedef long long LL;
 19 const int MAXN = 10011;
 20 const int MAXM = 50011;
 21 int n,m;
 22 int ecnt,cnt,total;
 23 int first[MAXN],next[MAXM],to[MAXM];
 24 int belong[MAXN];
 25 int dfn[MAXN],low[MAXN];
 26 bool pd[MAXN];
 27 int Stack[MAXN],top;
 28 int out[MAXN];
 29 int ans,jilu;
 30 
 31 inline int getint()
 32 {
 33        int w=0,q=0;
 34        char c=getchar();
 35        while((c<‘0‘ || c>‘9‘) && c!=‘-‘) c=getchar();
 36        if (c==‘-‘)  q=1, c=getchar();
 37        while (c>=‘0‘ && c<=‘9‘) w=w*10+c-‘0‘, c=getchar();
 38        return q ? -w : w;
 39 }
 40 
 41 inline void Init(){
 42     ecnt=0; cnt=0; total=0; top=0;
 43     memset(first,0,sizeof(first));
 44     memset(pd,0,sizeof(pd));
 45     memset(dfn,0,sizeof(dfn));
 46     memset(Stack,0,sizeof(Stack));
 47 }
 48 
 49 inline void link(int x,int y){
 50     next[++ecnt]=first[x]; first[x]=ecnt; to[ecnt]=y;
 51 }
 52 
 53 inline void dfs(int x){
 54     dfn[x]=++total; low[x]=dfn[x];
 55     pd[x]=1;
 56     Stack[++top]=x;
 57     for(int i=first[x];i;i=next[i]) {
 58     int v=to[i];
 59     if(!dfn[v]) {
 60         dfs(v);
 61         low[x]=min(low[x],low[v]);
 62     }
 63     else if(pd[v] && low[v]<low[x]) low[x]=low[v];
 64     }
 65     if(dfn[x]==low[x]) {
 66     cnt++;
 67     int now=Stack[top];
 68     do{
 69         belong[now]=cnt;
 70         pd[now]=0; top--;
 71         if(now==x) break;       
 72         now=Stack[top];
 73     }while(1);
 74     }
 75 }
 76 
 77 inline void tarjan(){
 78     for(int i=1;i<=n;i++) if(!dfn[i]) dfs(i);
 79 }
 80 
 81 inline void solve(){
 82     while(scanf("%d%d",&n,&m)!=EOF) {
 83     Init();
 84     int x,y;
 85     for(int i=1;i<=m;i++) {
 86         x=getint(); y=getint();
 87         link(x,y);
 88     }
 89     tarjan();
 90     for(int i=1;i<=n;i++){
 91         for(int j=first[i];j;j=next[j]) {
 92         int v=to[j];
 93         if(belong[v]!=belong[i]) {
 94             out[belong[i]]++;
 95         }
 96         }
 97     }
 98     ans=0,jilu=0;
 99     for(int i=1;i<=cnt;i++){
100         if(out[i]==0) {
101         ans++; jilu=i;
102         }
103     }
104     if(ans==1) {
105         ans=0;
106         for(int i=1;i<=n;i++) {
107         if(belong[i]==jilu) ans++;
108         }
109         printf("%d\n",ans);
110     }
111     else printf("0\n");
112     }
113 }
114 
115 int main()
116 {
117   solve();
118   return 0;
119 }