這題只能對每一個點查一遍……
有向圖的話能用floyd，可是迫於時限用了SPFA。
[delphi]
Program aa;
const
maxk=10000;
maxn=10000;
maxm=10000;
var
k,n,m,i,j,l:longint;
a:array[1..maxk] of longint;
q:array[1..maxn] of longint;
edge,next,head:array[1..maxm] of longint;
size:longint;
res,num,b:array[1..maxn] of boolean;
procedure add(u,v:longint);
begin
inc(size);
edge[size]:=v;
next[size]:=head[u];
head[u]:=size;
end;
procedure spfa;
var
i,j,p,now,v:longint;
begin
i:=1;j:=1;
while (i<=j) do
begin
now:=q[i];
p:=head[now];
while p<>0 do
begin
v:=edge[p];
if not(b[v]) then
begin
b[v]:=true;
inc(j);
q[j]:=v;
end;
p:=next[p];
end;
inc(i);
end;
for i:=1 to n do
res[i]:=res[i] and b[i];
end;
begin
size:=0;
fillchar(head,sizeof(head),0);
fillchar(edge,sizeof(edge),0);
fillchar(next,sizeof(next),0);
fillchar(b,sizeof(b),false);
fillchar(res,sizeof(res),true);
fillchar(num,sizeof(num),false);
read(k,n,m);
for i:=1 to k do read(a[i]);
for i:=1 to m do
begin
read(j,l);
add(j,l);
end;
for i:=1 to k do
if not(num[a[i]]) then
begin
num[a[i]]:=true;
q[1]:=a[i];
fillchar(b,sizeof(b),false);
b[q[1]]:=true;
spfa;
end; www.2cto.com
l:=0;
for i:=1 to n do if res[i] then inc(l);
writeln(l);
end.
