题意其实就是说有很多个点，求一组边把它们都连接起来，并且最大的那条边最小。很明显这就是一个最小生成树，是一颗保证最长边最短的树。

代码

刚刚学了个Borůvka算法，于是写了两个。

Borůvka

#include<cstdio>
#include<cctype>
#include<cstring>
#include<algorithm>
#include<cmath>
#define Pow(x) ((x)*(x))
using namespace std;
int read() {int x=0,f=1;char c=getchar();for (;!isdigit(c);c=getchar()) if (c=='-') f=-1;for (;isdigit(c);c=getchar()) x=x*10+c-'0';return x*f;
}
const int maxh=505;
const int maxn=1e3+10;
const int maxm=maxn*maxn;
int jp[maxh],n,m,all,f[maxn],close[maxn];
struct node {double x,y;
} a[maxn];
struct bian {int u,v;double w;
} e[maxm];
double dist(node &a,node &b) {return sqrt(Pow(a.x-b.x)+Pow(a.y-b.y));
}
int find(int x) {return f[x]==x?x:f[x]=find(f[x]);
}
double boruvka() {for (int i=1;i<=n;++i) f[i]=i;e[0].w=1e300;double ret=0;for (int t=n;t>1;) {memset(close,0,sizeof close);for (int i=1;i<=all;++i) if (find(e[i].u)!=find(e[i].v)) {int fx=find(e[i].u),fy=find(e[i].v);if (e[i].w<e[close[fx]].w) close[fx]=i;if (e[i].w<e[close[fy]].w) close[fy]=i;}for (int i=1;i<=n;++i) if (find(i)==i && close[i]) {int x=find(e[close[i]].u),y=find(e[close[i]].v);if (x!=y) f[x]=y,ret=max(ret,e[close[i]].w),--t;}}return ret;
}
int main() {
#ifndef ONLINE_JUDGEfreopen("test.in","r",stdin);freopen("my.out","w",stdout);
#endifm=read();for (int i=1;i<=m;++i) jp[i]=read();n=read(),all=0;for (int i=1;i<=n;++i) a[i].x=read(),a[i].y=read();for (int i=1;i<=n;++i) for (int j=i+1;j<=n;++j) e[++all]=(bian){i,j,dist(a[i],a[j])};double mst=boruvka();int ans=0;for (int i=1;i<=m;++i) ans+=(jp[i]>=mst);printf("%d\n",ans);return 0;
}

Kruskal

#include<cstdio>
#include<cctype>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
const int maxh=505;
const int maxn=1e3+10;
const int maxm=maxn*maxn;
struct bian {int u,v;double w;inline bool operator < (const bian &a) const {return w<a.w;}
} e[maxm];
struct P {double x,y;
} a[maxn];
double jp[maxn];
int f[maxn];
int find(int x) {return f[x]==x?f[x]:f[x]=find(f[x]);
}
double dist(P &a,P &b) {return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int main() {
#ifndef ONLINE_JUDGEfreopen("test.in","r",stdin);freopen("std.out","w",stdout);
#endifint n,m;scanf("%d",&m);for (int i=1;i<=m;++i) scanf("%lf",jp+i);scanf("%d",&n);for (int i=1;i<=n;++i) scanf("%lf%lf",&a[i].x,&a[i].y);int all=0;double mst=0;for (int i=1;i<=n;++i) for (int j=i+1;j<=n;++j) e[++all]=(bian){i,j,dist(a[i],a[j])};sort(e+1,e+all+1);for (int i=1;i<=n;++i) f[i]=i;for (int i=1,j=0;i<=all && j<n;++i) {int u=e[i].u,v=e[i].v,fx=find(u),fy=find(v);double w=e[i].w;if (fx!=fy) {f[fx]=fy;mst=max(mst,w);++j;}}int ans=0;for (int i=1;i<=m;++i) if (jp[i]>=mst) ++ans;printf("%d\n",ans);return 0;
}