bzoj 1051 tarjan强连通分量

/**************************************************************
Problem: 1051
User: BLADEVIL
Language: Pascal
Result: Accepted
Time:124 ms
Memory:1396 kb
****************************************************************/

//By BLADEVIL
var
n, m                        :longint;
pre, other                  :array[0..100010] of longint;
last                        :array[0..20010] of longint;
l                           :longint;
flag                        :array[0..10010] of boolean;
dfn, low                    :array[0..10010] of longint;
time                        :longint;
tot                         :longint;
stack                       :array[0..10010] of longint;
key                         :array[0..10010] of longint;
size                        :array[0..10010] of longint;
full                        :longint;
father                      :array[0..20010] of longint;

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

procedure connect(x,y:longint);
begin
inc(l);
pre[l]:=last[x];
last[x]:=l;
other[l]:=y;
end;

procedure init;
var
i                           :longint;
x, y                        :longint;
begin
read(n,m);
for i:=1 to m do
begin
read(x,y);
connect(y,x);
end;
end;

procedure dfs(x:longint);
var
q, p                        :longint;
cur                         :longint;
begin
inc(time);
dfn[x]:=time;
low[x]:=time;
flag[x]:=true;
inc(tot);
stack[tot]:=x;

q:=last[x];
while q<>0 do
begin
p:=other[q];
if dfn[p]=0 then
begin
dfs(p);
low[x]:=min(low[x],low[p]);
end else
if flag[p] then low[x]:=min(low[x],dfn[p]);
q:=pre[q];
end;

cur:=-1;
if dfn[x]=low[x] then
begin
while cur<>x do
begin
cur:=stack[tot];
dec(tot);
flag[cur]:=false;
key[cur]:=x+n;
inc(size[key[cur]]);
end;
end;
end;

procedure main;
var
i                           :longint;
q, p                        :longint;
begin
for i:=1 to n do if dfn[i]=0 then dfs(i);
for i:=1 to n do
begin
q:=last[i];
while q<>0 do
begin
p:=other[q];
if key[i]<>key[p] then
begin
connect(key[i],key[p]);
father[key[p]]:=key[i];
end;
q:=pre[q];
end;
end;
full:=-1;
for i:=1 to n do
begin
if (father[key[i]]=0) and (full=-1) then full:=key[i];
if (father[key[i]]=0) and (full<>-1) and (full<>key[i]) then
begin
writeln(0);
exit;
end;
end;
writeln(size[full]);
end;

begin
init;
main;
end.