HAOI2006 Popular cattle (strong Unicom component)

After the strong Unicom component is determined to determine the degree of 0 points there are several, there are 1 output this component of the number of points, otherwise output 0;

varI,j,n,m,x,y,ans1,ans2,t,cnt,top:longint; HEAD,NEXT,GO,STA,INP:Array[0..50010] ofLongint; Low,dfn,scc,s:Array[0..10000] ofLongint; Flag:Array[0..10000] ofBoolean; functionmin (x,y:longint): Longint; begin     ifX<y ThenExit (x)Elseexit (y); End;procedureDFS (k:longint);varI,v,x:longint;beginInc (T);d Fn[k]:=t;low[k]:=T; Inc (top); Sta[top]:=k; I:=Head[k]; whileI<>0  Do  beginV:=Go[i]; ifdfn[v]=0  Then    beginDfs (v); LOW[K]:=min (low[k],low[v]); End   Else ifscc[v]=0  Thenlow[k]:=min (low[k],dfn[v]); I:=Next[i]; End; ifLOW[K]=DFN[K] Then  beginInc (CNT); Repeatx:=sta[top];inc (s[cnt]);    Dec (top); SCC[X]:=CNT; ifX=k ThenBreak ; untilfalse; End; End;procedureInit;beginreadln (n,m); fori:=1  toM Do  beginreadln (x, y); Go[i]:=y;next[i]:=head[x];head[x]:=i; End;  fori:=1  toN Do  ifdfn[i]=0  ThenDFS (i);End;proceduremain;beginFillchar (flag,sizeof (flag), true); fori:=1  toN Do  beginJ:=Head[i];  whileJ<>0  Do     beginx:=Go[j]; ifScc[x]<>scc[i] Thenflag[scc[i]]:=false; J:=Next[j]; End; End;  fori:=1  toCnt Do  ifFlag[i] Then   beginInc (ANS1); Ans2:=S[i]; End; ifans1=1  ThenWriteln (ANS2)ElseWriteln (0); End;begininit; main;End.