子集枚举好题UVA1354

题目

分析:枚举子集以及关于该子集的补集，然后用子集去暴力构造一颗二叉树，注意左边的最远距离不一定来自于左子树，右边的最远距离也不一定来自于右子树

 #include "iostream"
 #include "cstdio"
 #include "cstring"
 #include "string"
 #include "vector"
 using namespace std;
 const int maxn=;
 int T,s,vis[<<maxn];
 double r,w[maxn],sum[<<maxn];
 struct Tree{
     double L,R;
     Tree():L(),R(){};
 };
 vector<Tree> tree[<<maxn];
 
 void dfs(int subset){
     if(vis[subset])  return;
     vis[subset]=;
     int flag=;
     for(int left=(subset-)&subset;left;left=(left-)&subset){
         flag=;
         int right=left^subset;
         double d1=sum[right]/sum[subset];
         double d2=sum[left]/sum[subset];
         dfs(left); dfs(right);
         for(int i=;i<tree[left].size();i++){
             for(int j=;j<tree[right].size();j++){
                 Tree t;
                 t.L=max(tree[left][i].L+d1,tree[right][j].L-d2);
                 t.R=max(tree[left][i].R-d1,tree[right][j].R+d2);
                 if(t.L+t.R<r)  tree[subset].push_back(t);
             }
         }
     }
     if(!flag)  tree[subset].push_back(Tree());
 }
 int main()
 {
     scanf("%d",&T);
     while(T--){
         scanf("%lf%d",&r,&s);
         for(int i=;i<s;i++)
             cin>>w[i];
         for(int i=;i<<<s;i++){
             tree[i].clear();
             sum[i]=;
             for(int j=;j<s;j++){
                 if(i&(<<j)){
                     sum[i]+=w[j];
                 }
             }
         }
         int root=(<<s)-;
         memset(vis,,sizeof(vis));
         dfs(root);
         double ans=-;
         for(int i=;i<tree[root].size();i++)
             ans=max(ans,tree[root][i].L+tree[root][i].R);
         if(ans==-)
             printf("-1\n");
         else
             printf("%.10lf\n",ans);
     }
 }