01背包方案数（变种题）Stone game--The Preliminary Contest for ICPC Asia Shanghai 2019

题意：https://nanti.jisuanke.com/t/41420

给你n个石子的重量，要求满足（Sum<=2*sum<=Sum+min)的方案数，min是你手里的最小值。

思路：

从最大重量的石子开始背包，每次ans+=dp【j-v【i】】就行了。

#define IOS ios_base::sync_with_stdio(0); cin.tie(0);
#include <cstdio>//sprintf islower isupper
#include <cstdlib>//malloc  exit strcat itoa system("cls")
#include <iostream>//pair
#include <fstream>//freopen("C:\Users\13606\Desktop\草稿.txt","r",stdin);
#include <bitset>
//#include <map>
//#include<unordered_map>
#include <vector>
#include <stack>
#include <set>
#include <string.h>//strstr substr
#include <string>
#include <time.h>//srand(((unsigned)time(NULL))); Seed n=rand()%10 - 0~9;
#include <cmath>
#include <deque>
#include <queue>//priority_queue<int, vector<int>, greater<int> > q;//less
#include <vector>//emplace_back
//#include <math.h>
//#include <windows.h>//reverse(a,a+len);// ~ ! ~ ! floor
#include <algorithm>//sort + unique : sz=unique(b+1,b+n+1)-(b+1);+nth_element(first, nth, last, compare)
using namespace std;//next_permutation(a+1,a+1+n);//prev_permutation
#define rint register int
#define fo(a,b,c) for(rint a=b;a<=c;++a)
#define fr(a,b,c) for(rint a=b;a>=c;--a)
#define mem(a,b) memset(a,b,sizeof(a))
#define pr printf
#define sc scanf
#define ls rt<<1
#define rs rt<<1|1
typedef long long ll;
void swapp(int &a,int &b);
double fabss(double a);
int maxx(int a,int b);
int minn(int a,int b);
int Del_bit_1(int n);
int lowbit(int n);
int abss(int a);
const double E=2.718281828;
const double PI=acos(-1.0);
//const ll INF=(1LL<<60);
const int inf=(1<<30);
const double ESP=1e-9;
const int mod=(int)1e9+7;
const int N=(int)1e6+10;

int v[N],dp[N];
void Init(int _[],int n)
{
    for(int i=1;i<=n;++i)
        _[i]=0;
}

void PR(int _[],int n)
{
    for(int i=1;i<=n;++i)
        pr("%d ",_[i]);
    pr("
");
}

bool J(int sum,int x,int min_)
{
    return 2*x>=sum&&2*x<=sum+min_;
}

int main()
{
    int T;
    sc("%d",&T);
    while(T--)
    {
        int n,sum=0;
        sc("%d",&n);
        for(int i=1;i<=n;++i)
            sc("%d",&v[i]),sum+=v[i];
        sort(v+1,v+1+n);
        Init(dp,sum);

        ll ans=0;
        dp[0]=1;
        for(int i=n;i>=1;--i)
        {
            for(int j=sum;j>=v[i];--j)
                if(dp[j-v[i]])
                {
                    dp[j]+=dp[j-v[i]];
                    dp[j]%=mod;
                    ans+=J(sum,j,v[i])?dp[j-v[i]]:0;
                    ans%=mod;
                }
        }
        pr("%lld
",ans);
    }
    return 0;
}

/**************************************************************************************/

int maxx(int a,int b)
{
    return a>b?a:b;
}

void swapp(int &a,int &b)
{
    a^=b^=a^=b;
}

int lowbit(int n)
{
    return n&(-n);
}

int Del_bit_1(int n)
{
    return n&(n-1);
}

int abss(int a)
{
    return a>0?a:-a;
}

double fabss(double a)
{
    return a>0?a:-a;
}

int minn(int a,int b)
{
    return a<b?a:b;
}