#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=105;
const int mod=1e9+7;
int n,L,a[N],b[N];
int dp[N][N][2][2][N*10];
int calc(int i,int cnt,bool haveL,bool haveR,int val)
{
if(i) val+=a[i-1]*(2*cnt-haveL-haveR);
if(val>L) return 0;
int &res=dp[i][cnt][haveL][haveR][val];
if(res!=-1) return res;
if(i==n)
{
if(val>L||cnt!=1||!haveL||!haveR) return 0;
return 1;
}
res=0;
///new comp
(res+=calc(i+1,cnt+1,haveL,haveR,val)*(cnt+1-haveL-haveR)%mod)%=mod;
///new L
if(!haveL) (res+=calc(i+1,cnt+1,1,haveR,val))%=mod;
///new R
if(!haveR) (res+=calc(i+1,cnt+1,haveL,1,val))%=mod;
if(cnt)
{
///merge
if(cnt>=2) (res+=calc(i+1,cnt-1,haveL,haveR,val)*(cnt-1)%mod)%=mod;
///push front
(res+=calc(i+1,cnt,haveL,haveR,val)*(cnt-haveL)%mod)%=mod;
///push back
(res+=calc(i+1,cnt,haveL,haveR,val)*(cnt-haveR)%mod)%=mod;
///made L
if(!haveL) (res+=calc(i+1,cnt,1,haveR,val)%=mod;
///made R
if(!haveR) (res+=calc(i+1,cnt,haveL,1,val))%=mod;
}
//cout<<i<<' '<<cnt<<' '<<haveL<<' '<<haveR<<' '<<val<<'\n' ;
return res;
}
main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
memset(dp,-1,sizeof dp);
cin>>n>>L;
if(n==1) return cout<<1,0;
for(int i=0;i<n;i++) cin>>b[i];
sort(b,b+n);
for(int i=0;i<n;i++) a[i]=b[i+1]-b[i];
cout<<calc(0,0,0,0,0);
}
Compilation message
skyscraper.cpp: In function 'long long int calc(long long int, long long int, bool, bool, long long int)':
skyscraper.cpp:38:52: error: lvalue required as left operand of assignment
38 | if(!haveL) (res+=calc(i+1,cnt,1,haveR,val)%=mod;
| ^~~
skyscraper.cpp:38:55: error: expected ')' before ';' token
38 | if(!haveL) (res+=calc(i+1,cnt,1,haveR,val)%=mod;
| ~ ^
| )
skyscraper.cpp: At global scope:
skyscraper.cpp:46:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
46 | main()
| ^
