POJ-3977-Subset

这个题35的数据还是比较大，不过把它分为2堆进行枚举就可以承受了，比较狠的是abs需要自己手写，否则WA

代码：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
const long long inf=1LL<<60;
const int maxn=40;
const int maxm=1<<18;
struct Node
{
    long long sum;
    int num;
    Node(){}
    Node(long long sm,int snum):sum(sm),num(snum){}
    bool operator < (const Node &a)const
    {
        return sum<a.sum;
    }
}SA[maxm],S[maxm];
int n,m,cnt,ansn;
long long a[maxn],ans;
vector<long long> A,B;
int cmp(Node a,Node b)
{
    if(a.sum==b.sum)
        return a.num<b.num;
    return a.sum<b.sum;
}
long long Abs(long long val)
{
    if(val<0)
        return -val;
    return val;
}
void InitSetA()
{
    int up=1<<m;
    for(int i=1;i<up;i++)
    {
        SA[i].sum=SA[i].num=0;
        for(int j=0;j<m;j++)
            if((i>>j)&1)
            {
                SA[i].sum+=A[j];
                SA[i].num++;
            }
        if(Abs(SA[i].sum)<ans)
        {    
            ans=Abs(SA[i].sum);
            ansn=SA[i].num;
        }
        else if(Abs(SA[i].sum)==ans)
        {
            ansn=min(ansn,SA[i].num);
        } 
    }   
    sort(SA+1,SA+up,cmp);
    cnt=0;
    S[cnt++]=SA[1];
    for(int i=2;i<up;i++)
        if(SA[i].sum!=SA[i-1].sum)
            S[cnt++]=SA[i];
}
void GetAns()
{
    int up=1<<(n-m),res=n-m,num;
    long long sum;
    for(int i=1;i<up;i++)
    {
        sum=num=0;
        for(int j=0;j<res;j++)
            if((i>>j)&1)
            {
                sum+=B[j];
                num++;
            }
        if(Abs(sum)<ans)
        {
            ans=Abs(sum);
            ansn=num;
        }
        else if(Abs(sum)==ans)
        {
            ansn=min(ansn,num);
        }
        int index=lower_bound(S,S+cnt,Node(-sum,num))-S;
        if(index<cnt)
        {
            if(Abs(sum+S[index].sum)<ans)
            {
                ans=Abs(sum+S[index].sum);
                ansn=num+S[index].num;
            }
            else if(Abs(sum+S[index].sum)==ans)
                ansn=min(ansn,num+S[index].num);
        }
        if(index>0)
        {
            if(Abs(sum+S[index-1].sum)<ans)
            {
                ans=Abs(sum+S[index-1].sum);
                ansn=num+S[index-1].num;
            }
            else if(Abs(sum+S[index-1].sum)==ans)
                ansn=min(ansn,num+S[index-1].num);
        }
    }
}
int main()
{
    while(scanf("%d",&n)&&n)
    {
        ans=inf;
        ansn=0;
        for(int i=0;i<n;i++)
            scanf("%I64d",&a[i]);
        m=(n+1)/2;
        A.clear();
        B.clear();
        for(int i=0;i<n;i++)
        {
            if(i<m)
                A.push_back(a[i]);
            else
                B.push_back(a[i]);
        }
        InitSetA();
        GetAns();
        printf("%I64d %d\n",ans,ansn);
    }
    return 0;
}