hdu 4756 最小生成树

最小生成树建图，然后枚举点，树上dp求出每个点对应的最小值。再统计答案。

#include <iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>#include<map>#include<vector>using namespace std;#define INF 2000000000#define N 1005double sum;double dis[N][N];double dp[N][N];bool vis[N][N];bool flag[N];double lowcost[N];int pre[N];struct node{    int x,y;};vector<int> tree[N];int n,m,num;struct point{double x,y;}p[1005];inline double g_dis(point &A,point &B){    return sqrt((A.x-B.x)*(A.x-B.x)+(A.y-B.y)*(A.y-B.y));}void prim(){    sum=0;    int i,j;    memset(flag,false,sizeof(flag));    for(i=1;i<=n;i++)    {        lowcost[i]=dis[1][i];        pre[i]=1;    }    flag[1]=true;    for(i=1;i<n;i++)    {        double mins=INF;        int v;        for(j=1;j<=n;j++)        {            if(flag[j] == false && lowcost[j] < mins)            {                mins=lowcost[j];                v=j;            }        }        sum+=mins;        vis[pre[v]][v] = vis[v][pre[v]] = true;        tree[v].push_back(pre[v]);        tree[pre[v]].push_back(v);        flag[v] = true;        for(j=1;j<=n;j++)        {            if(flag[j] == false && lowcost[j] > dis[v][j])            {                lowcost[j] = dis[v][j];                pre[j] = v;            }        }    }}double dfs(int root,int now,int fa=-1){    double ret = INF;    for(int i = 0;i<tree[now].size();i++)    {        int to=tree[now][i];        if(to!=fa){        double tmp = dfs(root,to,now);        ret=min(tmp,ret);        dp[now][to] = dp[to][now] = min(tmp,dp[now][to]);        }    }    if(root!=fa)        ret=min(ret,dis[root][now]);    return ret;}int main(){    int cas,k;    double x,y;    int i,j;    scanf("%d",&cas);    while(cas--)    {        scanf("%d%d",&n,&k);        for(i=1;i<=n;i++)        {            tree[i].clear();            scanf("%lf%lf",&x,&y);            p[i].x=x;p[i].y=y;            tree[i].clear();        }        for(i=1;i<=n;i++)        {            for(j=1;j<=n;j++)            {                vis[i][j]=false;                if(i==j) dis[i][j]=0;                else dis[i][j]=g_dis(p[i],p[j]);                dp[i][j]=INF;            }        }        prim();        double ans=sum;        for(i=1;i<=n;i++) dfs(i,i);        for(i=2;i<=n;i++)        {            for(j=2;j<i;j++)            {                if(vis[i][j])                {                    ans=max(ans,sum-dis[i][j]+dp[i][j]);                }            }        }        printf("%.2lf\n",ans*k);    }    return 0;}