POJ-1182 食物链

#include<cstdio>
#include<cstring>
using namespace std;
int n,d,sum;
int father[50010],relx[50010];
int find(int x)
{
    int rx;
    if (x!=father[x])
    {
        rx=find(father[x]);
        relx[x]=(relx[x]+relx[father[x]])%3;
        father[x]=rx;
    }
    return father[x];
}
int un(int x,int y)
{
    int rx=find(x),ry=find(y);
    if (rx==ry)
    {
        if ((relx[y]-relx[x]+3)%3==d-1) return 0;
        return 1;
    }
    father[ry]=rx;
    relx[ry]=(relx[x]-relx[y]+d+2)%3;
    return 0;
}
int main()
{
   int k,x,y,i;
   sum=0;
   scanf("%d%d",&n,&k);
   for (i=1;i<=n;i++) {father[i]=i;relx[i]=0;}
   while (k--)
   {
       scanf("%d%d%d",&d,&x,&y);
       if (x>n||y>n||(x==y&&d==2)) {sum++;continue;}
       if (un(x,y)==1) sum++;
   }
   printf("%d\n",sum);
}