POJ 2762 Going from u to v or from v to u? (Strongly connected component + topological sorting)

POJ 2762 Going from u to v or from v to u? (Strongly connected component + topological sorting)

Address: POJ 2762
First, scale down the point, and then determine whether the number of each layer of the topology network is 1 (I admit that if I do not know this question beforehand, I cannot think of it if I need to sort the topology ...). If there is a layer of 2, then the points of the two forks will not start from one point to another.
The Code is as follows:

#include 
  
   #include 
   
    #include 
    
     #include 
     
      #include #include 
      
       #include 
       #include 
        
         #include 
         
          using namespace std;#define LL __int64#define pi acos(-1.0)const int mod=1e9+7;const int INF=0x3f3f3f3f;const double eqs=1e-9;const int MAXN=1000+10;int head[MAXN], Ecnt, scc, top, indx;int low[MAXN], dfn[MAXN], belong[MAXN], stk[MAXN], instack[MAXN];struct node{ int u, v, next;}edge[7000];void add(int u, int v){ edge[Ecnt].v=v; edge[Ecnt].next=head[u]; head[u]=Ecnt++;}void tarjan(int u){ low[u]=dfn[u]=++indx; instack[u]=1; stk[++top]=u; for(int i=head[u];i!=-1;i=edge[i].next){ int v=edge[i].v; if(!dfn[v]){ tarjan(v); low[u]=min(low[u],low[v]); } else if(instack[v]){ low[u]=min(low[u],dfn[v]); } } if(low[u]==dfn[u]){ scc++; while(1){ int v=stk[top--]; belong[v]=scc; instack[v]=0; if(u==v) break; } }}void init(){ memset(head,-1,sizeof(head)); memset(dfn,0,sizeof(dfn)); memset(instack,0,sizeof(instack)); Ecnt=top=indx=scc=0;}int head1[MAXN], Ecnt1, deg[MAXN];struct node1{ int u, v, next;}edge1[7000];void add1(int u, int v){ edge1[Ecnt1].v=v; edge1[Ecnt1].next=head1[u]; head1[u]=Ecnt1++;}bool topo(int scc){ int i, u, tot, m=scc; while(m--){ tot=0; for(i=1;i<=scc;i++){ if(!deg[i]){ tot++; u=i; deg[i]--; } } if(tot>1) return false; for(i=head1[u];i!=-1;i=edge1[i].next){ deg[edge1[i].v]--; } } return true;}void init1(){ memset(deg,0,sizeof(deg)); memset(head1,-1,sizeof(head1)); Ecnt1=0;}int main(){ int n, m, i, j, u, v, t, f; scanf("%d",&t); while(t--){ scanf("%d%d",&n,&m); init(); while(m--){ scanf("%d%d",&u,&v); add(u,v); } for(i=1;i<=n;i++){ if(!dfn[i]) tarjan(i); } init1(); for(i=1;i<=n;i++){ for(j=head[i];j!=-1;j=edge[j].next){ v=edge[j].v; if(belong[i]!=belong[v]){ add1(belong[i],belong[v]); deg[belong[v]]++; //printf("%d %d\n",belong[i],belong[v]); } } } if(topo(scc)) puts("Yes"); else puts("No"); } return 0;}