hdu4081 Qin Shi Huang's National Road System PRIM+dp

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代码1：

#include<cstdio>#include<cstdlib>#include<cmath>#include<iostream>#include<vector>using namespace std;const int N = 1000 + 10;const double INF = 1.0*1e8;struct point{    double x,y;    double val;}p[N];double get_dis(point a,point b){    return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) );}vector<int> ed[N];double map[N][N];int n,pre[N];double dis[N];double sum;void prim(){    int now=1;    for(int i=1;i<=n;i++) ed[i].clear();    for(int i=1;i<=n;i++) dis[i] = 1.0*INF;    for(int i=1;i<=n;i++)    {        for(int j=1;j<=n;j++) if(now!=j && dis[j]>0 && map[now][j]>=0 && dis[j]>map[now][j]){            dis[j] = map[now][j];            pre[j] = now;        }        dis[now] = -1.0;        int min_p=-1;        double min_dis=1.0*INF;        for(int j=1;j<=n;j++) if(dis[j]>0){            if(dis[j] < min_dis)            {                min_p = j;                min_dis = dis[j];            }        }        if(min_p < 0) break;        sum += min_dis;        ed[min_p].push_back(pre[min_p]);        ed[pre[min_p]].push_back(min_p);        now = min_p;    }}double dfs(int x,int fa){    double max_val=p[x].val;    for(int i=0;i<ed[x].size();i++)    {        int j = ed[x][i];        if(j!=fa)        {            max_val = max( max_val,dfs(j,x) );        }    }    return max_val;}int main(){    int t;    cin>>t;    while(t--)    {        sum = 0;        scanf("%d",&n);        for(int i=1;i<=n;i++)            scanf("%lf%lf%lf",&p[i].x,&p[i].y,&p[i].val);        for(int i=1;i<=n;i++)            for(int j=1;j<=n;j++)                if(i!=j)                    map[i][j] = get_dis(p[i],p[j]);                else                    map[i][j] = 0.0;        prim();        double ans = 0;        for(int i=1;i<=n;i++)            for(int j=0;j<ed[i].size();j++)            {                int k = ed[i][j];                double s1 = dfs(i,k);                double s2 = dfs(k,i);                ans = max(ans, (s1+s2)/(sum - map[i][k]));            }        ans += 1e-8;        printf("%.2lf\n",ans);    }    return 0;}

代码2：

#include<cstdio>#include<cstdlib>#include<cmath>#include<iostream>#include<vector>#include<cstring>using namespace std;const int N = 1000 + 10;const double INF = 1.0*1e8;struct point{    double x,y;    double val;}p[N];double get_dis(point a,point b){    return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) );}vector<int> ed[N];double map[N][N];int n,pre[N],vis[N];double dis[N],maxcost[N][N];double sum;void prim(){    int now=1;    for(int i=1;i<=n;i++) ed[i].clear();    for(int i=1;i<=n;i++) dis[i] = 1.0*INF;    for(int i=1;i<=n;i++)    {        for(int j=1;j<=n;j++) if(now!=j && dis[j]>0 && map[now][j]>=0 && dis[j]>map[now][j]){            dis[j] = map[now][j];            pre[j] = now;        }        dis[now] = -1.0;        int min_p=-1;        double min_dis=1.0*INF;        for(int j=1;j<=n;j++) if(dis[j]>0){            if(dis[j] < min_dis)            {                min_p = j;                min_dis = dis[j];            }        }        if(min_p < 0) break;        sum += min_dis;        ed[min_p].push_back(pre[min_p]);        ed[pre[min_p]].push_back(min_p);        now = min_p;    }}void dfs(int s,int x){    for(int i=0;i<ed[x].size();i++){        int v = ed[x][i];        //printf("%d->%d\n",x,v);        if(vis[v]) continue;        vis[v] = 1;        maxcost[s][v] = max(maxcost[s][v] , max(map[x][v],maxcost[s][x]));        dfs(s,v);    }}int main(){    int t;    cin>>t;    while(t--)    {        sum = 0;        scanf("%d",&n);        for(int i=1;i<=n;i++)            scanf("%lf%lf%lf",&p[i].x,&p[i].y,&p[i].val);        for(int i=1;i<=n;i++)            for(int j=1;j<=n;j++)                if(i!=j)                    map[i][j] = get_dis(p[i],p[j]);                else                    map[i][j] = 0.0;        prim();        double ans = 0;        //cout<<"hehe\n";        for(int i=1;i<=n;i++) for(int j=1;j<=n;j++) maxcost[i][j] = 0;        for(int i=1;i<=n;i++){            memset(vis,0,sizeof(vis));            vis[i] = 1;            maxcost[i][i] = 0;            dfs(i,i);        }        //printf("orz\n");        for(int i=1;i<=n;i++)            for(int j=i+1;j<=n;j++)            {                ans = max(ans, (p[i].val+p[j].val)/(sum-maxcost[i][j])  );            }        ans += 1e-8;        printf("%.2lf\n",ans);    }    return 0;}

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