博弈动归，方程f[i]=pool[i]-max{f[next[i]]}，从后往前推，next[i]表示可能为i的后继的值。
CODE:
/*
AUTHOR: Su Jiao
DATE: 2010-6-18
DESCRIPTION:
http://acm.pku.edu.cn/JudgeOnline/problem?id=1678
*/
#include <iostream>
using std::cin;
using std::cout;
using std::endl;
#include <vector>
using std::vector;
#include <algorithm>
using std::sort;
class Application
{
int t,n,a,b;
vector<int> pool;
int get()
{
const int oo=~(1<<31);
sort(pool.begin(),pool.end());
//f[i]=pool[i]-max{f[next[i]]}
vector<int> f(n,-oo);
int answer=-oo;
bool have_first=false;
for (int i=n-1;i>=0;i–)
{
bool have_next=false;
for (int j=i+1;j<n;j++)
if (a<=pool[j]-pool[i]
&&pool[j]-pool[i]<=b
&&f[i]<f[j])
f[i]=f[j],
have_next=true;
if (have_next) f[i]=pool[i]-f[i];
else f[i]=pool[i];
if (a<=pool[i]
&&pool[i]<=b
&&answer<f[i])
answer=f[i],
have_first=true;
}
if (!have_first) answer=0;
return answer;
}
public:
Application()
{
std::ios::sync_with_stdio(false);
}
int run()
{
cin>>t;
for (int i=0;i<t;i++)
{
cin>>n>>a>>b;
pool.resize(n);
for (int j=0;j<n;j++)
cin>>pool[j];
cout<<get()<<endl;
pool.clear();
}
return 0;
}
};
int main()
{
Application app;
return app.run();
}