uva 10397 Connect the Campus（最小生成树）

#include <iostream>
#include <algorithm>
#include <utility>
#include <cstring>
#include <cmath>
#include <cstdio>
using namespace std;
#define INF 9999999
typedef pair<double,double> P;
P point[800];
double grap[800][800];
double dis[800];
bool used[800];
int N,M;

double prim()
{
memset(used,false,sizeof(used));
for(int i = 0; i < N; ++i)
dis[i] = INF;
dis[0] = 0;
double res = 0;

while(true)
{
int v = -1;
for(int u = 0; u < N; ++u)
if(!used[u] && (v == -1 || dis[v] > dis[u]))
v = u;
if(v == -1)
break;

used[v] = true;
res += dis[v];

for(int u = 0; u < N; ++u)
dis[u] = min(dis[u],grap[v][u]);
}

return res;
}

int main()
{
while(cin >> N)
{
for(int i = 0; i < N; ++i)
cin >> point[i].first >> point[i].second;
cin >> M;
memset(grap,-1,sizeof(grap));
int a,b;
for(int i = 0; i < M; ++i)
{
cin >> a >> b;
grap[a-1][b-1] = grap[b-1][a-1] = 0;
}

for(int i = 0; i < N; ++i)
{
grap[i][i] = 0;
for(int j = i+1; j < N; ++j)
{
if(grap[i][j] != 0)
{
grap[i][j] = grap[j][i] =
sqrt((point[i].first-point[j].first)*(point[i].first-point[j].first)
+ (point[i].second-point[j].second)*(point[i].second-point[j].second));
}
}
}
printf("%.2f\n",prim());
}
return 0;
}