Luogu P3535 [POI2012]TOU-Tour de Byteotia 题解

#include<bits/stdc++.h>
using namespace std;
inline int read(){
    int res=0,f=1;char ch=getchar();while(ch<'0'ch>'9'){if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0'&&ch<='9') res=res*10+ch-'0',ch=getchar();return res*f;
}
int n,m,k,fa[1000010],ans,x[1000010],y[1000010];
inline int getfa(int x){return fa[x]==x?x:fa[x]=getfa(fa[x]);}
inline void merge(int x,int y){
    x=getfa(x);
    y=getfa(y);
    if(x==y) ;
    else fa[y]=x;
} 
int main(){
    n=read();m=read();k=read();
    for(int i=1;i<=n;i++) fa[i]=i;
    for(int i=1;i<=m;i++){
        x[i]=read();y[i]=read();
        if(x[i]>k&&y[i]>k) merge(x[i],y[i]);
    }
    for(int i=1;i<=m;i++){
        if(x[i]>k&&y[i]>k) continue ;
        x[i]=getfa(x[i]);y[i]=getfa(y[i]);
        if(x[i]==y[i]) ans++;
        else merge(x[i],y[i]);
    }
    printf("%d\n",ans);
    return 0;
}