[BZOJ1654] [Usaco2006 Jan]The Cow Prom 奶牛舞会

传送门

http://www.lydsy.com/JudgeOnline/problem.php?id=1654

题目大意

求图中包括点数大于1的强连通分量数

题解

模板测试

var
 w:array[0..70000,1..2]of longint;
 low,dfn,p,t:array[0..10005]of longint;
 i,j,k:longint;
 n,m,len,a,b,tmp,ans:longint;
procedure init(a,b:longint);
begin
 w[len,1]:=b;
 if w[a,2]=0
 then w[a,2]:=len else w[w[a,1],2]:=len;
 w[a,1]:=len; inc(len);
end;

function min(a,b:longint):longint;
begin
 if a>b then exit(b) else exit(a);
end;

procedure tarjan(a:longint);
var tt,s:longint;
begin
 dfn[a]:=tmp; low[a]:=tmp; inc(tmp);
 inc(t[0]); t[t[0]]:=a; p[a]:=1;
 tt:=w[a,2];
 while tt<>0 do
  begin
   if dfn[w[tt,1]]=0
   then begin tarjan(w[tt,1]); low[a]:=min(low[a],low[w[tt,1]]); end
   else if p[w[tt,1]]=1 then low[a]:=min(low[a],dfn[w[tt,1]]);
   tt:=w[tt,2];
  end;
 s:=t[0];
 if dfn[a]=low[a] then begin
  repeat
   p[t[t[0]]]:=0;
   dec(t[0]);
  until a=t[t[0]+1];
  if t[0]<>s-1 then inc(ans);
 end;
end;

begin
 readln(n,m); len:=n+1;
 for i:=1 to m do
  begin readln(a,b); init(a,b); end;
 tmp:=1; ans:=0;
 for i:=1 to n do
  if dfn[i]=0 then tarjan(i);
 writeln(ans);
end.