Strongly Connected HDU 1269

N point M side

Determine whether a-> B->

Strongly Connected Component equal to 1

 1 #include<stdio.h> 2 #include<algorithm> 3 #include<string.h> 4 #include<queue> 5 #include<math.h> 6 #include<stack> 7  8 using namespace std; 9 10 #define MAXN 10001011 12 int head[MAXN],low[MAXN],dfn[MAXN],f[MAXN];13 bool vis[MAXN];14 int cnt,k,num;15 struct edg16 {17     int fr,to,next;18 19 }x[MAXN];20 21 void add(int u,int v)22 {23     x[cnt].next=head[u];24     x[cnt].fr=u;25     x[cnt].to=v;26     head[u]=cnt++;27 }28 stack<int>s;29 30 void dfs(int u)31 {32     low[u]=dfn[u]=k++;33     vis[u]=1;34     s.push(u);35     int i;36     for(i=head[u];i!=-1;i=x[i].next)37     {38         int t=x[i].to;39         if(!dfn[t])40         {41             dfs(t);42             low[u]=min(low[u],low[t]);43         }44         else if(vis[t])45             low[u]=min(low[u],dfn[t]);46     }47     if(low[u]==dfn[u])48     {49         num++;50         while(!s.empty())51         {52             int now=s.top();53             s.pop();54             vis[now]=0;55             f[now]=num;56             if(now==u)break;57         }58     }59 }60 int main()61 {62     int n,m;63 64     while(scanf("%d%d",&n,&m)!=EOF)65     {66         if(n+m==0)67             break;68         int i;69         memset(head,-1,sizeof(head));70         cnt=0;71         for(i=1;i<=m;i++)72         {73             int a,b;74             scanf("%d%d",&a,&b);75             add(a,b);76         }77         k=1;78         num=0;79         memset(dfn,0,sizeof(dfn));80         memset(low,0,sizeof(low));81         memset(vis,0,sizeof(vis));82         memset(f,0,sizeof(f));83         for(i=1;i<=n;i++)84         {85             if(!dfn[i])86                 dfs(i);87         }88         if(num==1)89             printf("Yes\n");90         else91             printf("No\n");92     }93     return 0;94 }

 

Strongly Connected HDU 1269