POJ 2728 （Desert King）

来源：互联网发布：虚拟定位ios软件编辑：程序博客网时间：2024/05/22 15:37

题意：最有比例生成树

最近做了好几道这样的二分答案求解的题，

#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>#include <queue>using namespace std;const int N = 1009;const int INF  = 0x3f3f3f3f;double  map[N][N];int re[N][3];double dis[N][N],mdis[N];bool visit[N];int high[N][N];int n;double setdis(int i,int j){    return sqrt(1.0*(re[i][0]-re[j][0])*(re[i][0]-re[j][0])+(re[i][1]-re[j][1])*(re[i][1]-re[j][1]));}void init(){    for(int i=0;i<n;i++)    {        scanf("%d%d%d",&re[i][0],&re[i][1],&re[i][2]);        for(int j=0;j<i;j++)        dis[i][j] = dis[j][i] = setdis(i,j),        high[i][j] = high[j][i] = abs(re[i][2]-re[j][2]);    }}bool oor(double m){    memset(visit,false,sizeof(visit));    for(int i=0;i<n;i++)    for(int j=0;j<i;j++)        map[i][j] = map[j][i] = high[i][j]-dis[i][j]*m;    double ans=0;    for(int i=1;i<n;i++)    mdis[i] = map[0][i];    mdis[0]=0;visit[0] = true;    while(1)    {        double mindis = 1e12;        int minone = -1;        for(int i=0;i<n;i++)        if(!visit[i]&&mdis[i]<mindis)        mindis = mdis[i],minone =i;        if(minone==-1)        return ans<=0;        ans+=mindis;        visit[minone] = true;        for(int i=1;i<n;i++)        if(!visit[i]&&mdis[i]>map[minone][i])        mdis[i] = map[minone][i];    }}void solve(){    double r = 1e12,l = 0,mid;    while((r-l)>0.00001)    {        mid = (l+r)/2;        if(oor(mid))        r = mid;        else        l = mid;    }    printf("%.3lf\n",mid);}int main(){    freopen("in.txt","r",stdin);    while(~scanf("%d",&n)&&n)    {        init();        solve();    }    return 0;}