NOI 2001 & luogu P2024 & POJ 1182食物链

 1 program foodchain;
 2 var
 3    n,k,i,x,a,b,ans:longint;
 4    uset,rel:array[0..50000] of longint;
 5 
 6 function find(app:longint):longint;
 7 var
 8   t:longint;
 9 begin
10   if uset[app]=0 then exit(app);
11   t:=find(uset[app]);
12   rel[app]:=(rel[app]+rel[uset[app]]) mod 3;
13   uset[app]:=t;
14   find:=uset[app];
15 end;
16 
17 function union(a,b:longint):boolean;
18 var
19   p1,p2:longint;
20 
21 begin
22   p1:=find(a);
23   p2:=find(b);
24   if p1=p2 then             //之前已经存在关系
25     if (rel[b]-rel[a]+3) mod 3<>x-1 then exit(false)
26       else exit(true);
27 
28   uset[p2]:=p1;
29   rel[p2]:=(rel[a]+3-rel[b]+x-1) mod 3;
30   exit(true);
31 end;
32 
33 begin
34     readln(n,k);
35 
36     for i:= 1 to k do
37       begin
38           readln(x,a,b);
39           if (a>n) or (b>n) or ((x=2) and (a=b)) then inc(ans)
40            else  if union(a,b)=false then inc(ans);
41       end;
42 
43     writeln(ans);
44 end.