题目：http://www.lydsy.com/JudgeOnline/problem.php?id=2429
题解：从某一点遍历n个点，且使最长边最短，就是MST了。
代码：
1 #include<cstdio> 2 3 #include<cstdlib> 4 5 #include<cmath> 6 7 #include<cstring> 8 9 #include<algorithm> 10 11 #include<iostream> 12 13 #include<vector> 14 15 #include<map> 16 17 #include<set> 18 19 #include<queue> 20 21 #include<string> 22 23 #define inf 1000000000 24 25 #define maxn 1000+5 26 27 #define maxm 200000+5 28 29 #define eps 1e-10 30 31 #define ll long long 32 33 #define pa pair<int,int> 34 35 #define for0(i,n) for(int i=0;i<=(n);i++) 36 37 #define for1(i,n) for(int i=1;i<=(n);i++) 38 39 #define for2(i,x,y) for(int i=(x);i<=(y);i++) 40 41 #define for3(i,x,y) for(int i=(x);i>=(y);i--) 42 43 #define for4(i,x) for(int i=head[x],y=e[i].go;i;i=e[i].next,y=e[i].go) 44 45 #define for5(n,m) for(int i=1;i<=n;i++)for(int j=1;j<=m;j++) 46 47 #define mod 1000000007 48 #define sqr(x) (x)*(x) 49 50 using namespace std; 51 52 inline int read() 53 54 { 55 56 int x=0,f=1;char ch=getchar(); 57 58 while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} 59 60 while(ch>='0'&&ch<='9'){x=10*x+ch-'0';ch=getchar();} 61 62 return x*f; 63 64 } 65 int n,m; 66 double mx,b[maxn],d[maxn]; 67 bool v[maxn]; 68 struct rec{int x,y;}a[maxn]; 69 priority_queue<pa,vector<pa>,greater<pa> >q; 70 inline double dist(int x,int y){return sqrt(sqr(a[x].x-a[y].x)+sqr(a[x].y-a[y].y));} 71 inline void prim() 72 { 73 for1(i,n)d[i]=inf; 74 d[1]=0; 75 q.push(pa(0,1)); 76 while(!q.empty()) 77 { 78 int x=q.top().second;q.pop(); 79 if(v[x])continue;v[x]=1; 80 if(d[x]>mx)mx=d[x]; 81 for1(i,n)if(!v[i]&&dist(i,x)<d[i]) 82 { 83 d[i]=dist(i,x); 84 q.push(pa(d[i],i)); 85 } 86 } 87 } 88 89 int main() 90 91 { 92 93 freopen("input.txt","r",stdin); 94 95 freopen("output.txt","w",stdout); 96 97 m=read(); 98 for1(i,m)b[i]=read(); 99 n=read(); 100 for1(i,n)a[i].x=read(),a[i].y=read(); 101 prim(); 102 int ans=0; 103 for1(i,m)if(b[i]>=mx)ans++; 104 cout<<ans<<endl; 105 106 return 0; 107 108 }