POJ 1182-eat

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简单的并查集的应用，经典题目：

{ Author:wzx961008
 Problem:POJ 1182-eat
 Verdict:Accepted
 Language:PASCAL
 Run Time:0.188s
 AC Date:2011-4-19
}
var i,n,k,d,x,y,ans,gx,fx,gy,fy:longint;
    f,g:array[1..50000]of longint;
function find(i:longint):longint;
begin
 if f[i]<>i then f[i]:=find(f[i]);
 exit(f[i]);
end;
function getrel(i:longint):longint;
begin
 if f[i]<>i then g[i]:=(getrel(f[i])+g[i]) mod 3;
 exit(g[i]);
end;
begin
 readln(n,k);
 for i:=1 to n do f[i]:=i;
 for i:=1 to k do begin
  readln(d,x,y); dec(d);
  if (x>n)or(y>n) then begin inc(ans); continue; end;
  gx:=getrel(x); fx:=find(x); gy:=getrel(y); fy:=find(y);
  if fx<>fy then begin
   f[fx]:=fy;
   g[fx]:=(d-gx+gy+3) mod 3;
  end else if (gx-gy+3) mod 3<>d then inc(ans);
 end;
 writeln(ans);
end.