"Strong Unicom component reduction" "Tarjan" bzoj1051 [HAOI2006] Popular Cattle

is to see if there are some points that can be reached from any other point

Theorem: The only point in a direction-free graph with a degree of 0 can be reached from any point.

So, if the point is zero (strong unicom component), the answer is the degree of the midpoint of the strong unicom component.

If not unique, the answer is 0, easy to pass.

Code (lazy Tarjan, used two times Dfs):

1#include <cstdio>2#include <cstring>3#include <vector>4 using namespacestd;5vector<int>order;6 intv[100001],first[100001],next[100001],en;7 inta[50001],b[50001],scc[10001],num[10001],sum,chu[10001];8 BOOLvis[10001];9 intn,m;TenInlinevoidAddedge (Const int&u,Const int&AMP;V) {v[++en]=v;next[en]=first[u];first[u]=en;} One voidClear () A { -memset (V,0,sizeof(v)); -memset (First,0,sizeof(first)); theMemset (Next,0,sizeof(next)); -en=0; - } - voidDfsintcur) + { -vis[cur]=true; +      for(intI=first[cur];i;i=Next[i]) A       if(!Vis[v[i]]) at DFS (V[i]); - order.push_back (cur); - } - voidDFS2 (intCurintsum) - { -vis[cur]=true; inscc[cur]=sum; -num[sum]++; to      for(intI=first[cur];i;i=Next[i]) +       if(!Vis[v[i]]) - DFS2 (v[i],sum); the } * voidScc () $ {Panax Notoginseng      for(intI=1; i<=n;i++) -       if(!Vis[i]) the DFS (i); +memset (Vis,false,sizeof(VIS)); Clear (); A      for(intI=1; i<=m;i++) Addedge (B[i],a[i]); the     intsz=order.size (); +      for(inti=sz-1; i>=0; i--) -       if(!Vis[order[i]]) $DFS2 (order[i],++sum); $ } - intExam () - { the     intCnt=0, Record; -      for(intI=1; i<=m;i++)Wuyi       if(scc[a[i]]!=Scc[b[i]]) thechu[scc[a[i]]]++; -      for(intI=1; i<=sum;i++) Wu       if(!Chu[i]) -         { Aboutcnt++; $record=i; -           if(cnt==2) -             return 0; -         } A     returnNum[record]; + } the intResCharC; -InlineintGet () $ { theres=0; C='*';  the      while(c<'0'|| C>'9') c=GetChar (); the      while(c>='0'&&c<='9') {res=res*Ten+ (C-'0'); C=GetChar ();} the     returnRes; - } in intMain () the { theN=get (); m=Get (); About      for(intI=1; i<=m;i++) {a[i]=get (); b[i]=Get (); Addedge (A[i],b[i]);} theSCC ();p rintf ("%d\n", Exam ()); the     return 0; the}

"Strong Unicom component reduction" "Tarjan" bzoj1051 [HAOI2006] Popular Cattle