【CF659E】New Reform

 1 var head,vet,next,flag:array[1..200000]of longint;
 2     n,m,x,y,tmp,ans,tot,i:longint;
 3 
 4 procedure add(a,b:longint);
 5 begin
 6  inc(tot);
 7  next[tot]:=head[a];
 8  vet[tot]:=b;
 9  head[a]:=tot;
10 end;
11 
12 procedure dfs(u,pre:longint);
13 var e,v:longint;
14 begin
15  if flag[u]=1 then begin tmp:=0; exit; end;
16  flag[u]:=1;
17  e:=head[u];
18  while e<>0 do
19  begin
20   v:=vet[e];
21   if v<>pre then dfs(v,u);
22   e:=next[e];
23  end;
24 end;
25 
26 begin
27 // assign(input,‘1.in‘); reset(input);
28  //assign(output,‘1.out‘); rewrite(output);
29  readln(n,m);
30  for i:=1 to m do
31  begin
32   read(x,y);
33   add(x,y);
34   add(y,x);
35  end;
36  for i:=1 to n do
37   if flag[i]=0 then
38   begin
39    tmp:=1;
40    dfs(i,0);
41    ans:=ans+tmp;
42   end;
43  writeln(ans);
44 // close(input);
45  //close(output);
46 end.