Luogu P2024 [NOI2001]食物链

#include
#include
using namespace std;

int n,k,fa[1000005],ans;

inline int getfa(int v){
    return fa[v]==v?v:fa[v]=getfa(fa[v]);
}

inline void merge(int x,int y){
    x=getfa(x);y=getfa(y);
    if(x!=y)fa[y]=x;
}

inline bool family(int x,int y){
    return getfa(x)==getfa(y);
}

int main(){
    scanf("%d%d",&n,&k);
    for(int i=1;i<=3*n;i++)fa[i]=i;
    for(int i=1;i<=k;i++){
        int opt,x,y;
        scanf("%d%d%d",&opt,&x,&y);
        if(x>n||y>n){ans++;continue;}
        if(opt==1){
            if(family(x,y+n)||family(x,y+2*n)){ans++;continue;}
            merge(x,y);
            merge(x+n,y+n);
            merge(x+2*n,y+2*n);
        }
        else{
            if(x==y){ans++;continue;}
            if(family(x+2*n,y)||family(x,y)){ans++;continue;}
            merge(x+n,y);
            merge(x,y+2*n);
            merge(x+2*n,y+n);//是个环：猎物的猎物是天敌 
        }
    }
    printf("%d\n",ans);
}
//x+n:猎物 x+2*n:天敌