BZOJ 3060 Kruskal

//By SiriusRen
#include <cstdio>
using namespace std;
#define N 2000005
int n,m,k,f[N],cnt;
struct Node{int from,to;}node[N];
int find(int x){return x==f[x]?x:f[x]=find(f[x]);}
int main(){
    scanf("%d%d%d",&n,&m,&k);
    for(int i=1;i<=m;i++)scanf("%d%d",&node[i].from,&node[i].to);
    for(int i=1;i<=n;i++)f[i]=i;
    for(int i=1;i<=m;i++){
        if(node[i].from>k&&node[i].to>k){
            int fx=find(node[i].from),fy=find(node[i].to);
            if(fx!=fy)f[fx]=fy;
            cnt++;
        }
    }
    for(int i=1;i<=m;i++){
        if(node[i].from<=k||node[i].to<=k){
            int fx=find(node[i].from),fy=find(node[i].to);
            if(fx!=fy)f[fx]=fy,cnt++;
        }
    }printf("%d\n",m-cnt);
}