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=15;
int T,s,vis[1<<maxn]; 
double r,w[maxn],sum[1<<maxn];
struct Tree{
    double L,R;
    Tree():L(0),R(0){};
};
vector<Tree> tree[1<<maxn];

void dfs(int subset){
    if(vis[subset])  return;
    vis[subset]=1;
    int flag=0;
    for(int left=(subset-1)&subset;left;left=(left-1)&subset){
        flag=1;
        int right=left^subset;
        double d1=sum[right]/sum[subset];
        double d2=sum[left]/sum[subset];
        dfs(left); dfs(right);
        for(int i=0;i<tree[left].size();i++){
            for(int j=0;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=0;i<s;i++)
            cin>>w[i];
        for(int i=0;i<1<<s;i++){
            tree[i].clear();
            sum[i]=0;
            for(int j=0;j<s;j++){
                if(i&(1<<j)){
                    sum[i]+=w[j];
                }
            }
        }
        int root=(1<<s)-1;
        memset(vis,0,sizeof(vis));
        dfs(root);
        double ans=-1;
        for(int i=0;i<tree[root].size();i++)
            ans=max(ans,tree[root][i].L+tree[root][i].R);
        if(ans==-1)
            printf("-1
");
        else
            printf("%.10lf
",ans);
    }
}