2016夏季练习——类次小生成树

来源：HDU4081

代码：

次优生成树

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
using namespace std;
const int INF = 0x3f3f3f3f;
const double MAXDOUBLE = INF*1.0;
int n;
const int MAXN = 1010;
struct Point{
double x,y;
}p[MAXN];
int ren[MAXN];
double mp[MAXN][MAXN];
double dist[MAXN];
int pre[MAXN];
int vis[MAXN];
double path[MAXN][MAXN];
bool used[MAXN][MAXN];
vector<int>vec[MAXN];
double dis(Point a,Point b){
return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
double mst;
void prim(){
mst=0;
double dm;
int dv;
memset(vis,0,sizeof(vis));
memset(dist,0,sizeof(dist));
memset(used,0,sizeof(used));
memset(path,0,sizeof(path));
for(int i=1;i<=n;i++){
dist[i] = mp[1][i];
pre[i] = 1;
}
vis[1] = 1;
dv=-1;
for(int i=1;i<n;i++){
dm = MAXDOUBLE;
dv = -1;
for(int j=1;j<=n;j++){
if(!vis[j]&&dm>dist[j]){
dm = dist[j];
dv = j;
}
}
used[pre[dv]][dv] = used[pre[dv]][dv] = true;
vis[dv]=1;
mst+=mp[pre[dv]][dv];
for(int j=1;j<=n;j++){
if(vis[j]&&j!=dv){
path[dv][j] = path[j][dv] = max(path[j][pre[dv]],dist[dv]);
}
if(!vis[j]&&dist[j]>mp[dv][j]){
dist[j] = mp[dv][j];
pre[j] = dv;
}
}
}
}
int main(){
int T;
scanf("%d",&T);
while(T--){
scanf("%d",&n);
for(int i=1;i<=n;i++){
scanf("%lf%lf%d",&p[i].x,&p[i].y,&ren[i]);
}
for(int i=1;i<=n;i++){
for(int j=1;j<=n;j++){
mp[i][j]=dis(p[i],p[j]);
}
mp[i][i] = 0.0;
}
for(int i=0;i<=n;i++)
vec[i].clear();
prim();
double ans=-MAXDOUBLE;
for(int i=1;i<=n;i++){
for(int j=1;j<=n;j++){
if(i!=j){
if(used[i][j]){
ans = max(ans,(ren[i]+ren[j])/(mst-mp[i][j]));
}
else
{
ans = max(ans,(ren[i]+ren[j])/(mst-path[i][j]));
}
}
}
}
printf("%.2f\n",ans);
}
return 0;
}