考场上空间开大了一倍就爆0了QAQ…
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn = 21;
int height[30], pos[30];
long long dp[1 << maxn][21];
int main()
{
int n, delta;
scanf("%d%d",&n,&delta);
for(int i = 1;i <= n + 1; ++i) pos[i] = (1 << (i - 1)) ;
for(int i = 1;i <= n; ++i) scanf("%d",&height[i]);
for(int i = 1;i <= n; ++i) dp[pos[i]][i] = 1;
for(int i = 1;i < pos[n + 1]; ++i)
{
for(int j = 1;j <= n; ++j)
{
if((i & pos[j]) == 0) continue;
int mx = i ^ pos[j];
if(mx == 0) continue;
for(int k = 1;k <= n; ++k)
{
if( (i & pos[k]) == 0 || k == j || abs(height[j] - height[k]) <= delta) continue;
dp[i][j] += dp[mx][k];
}
}
}
long long fin = 0;
for(int i = 1;i <= n; ++i) fin += dp[pos[n + 1] - 1][i];
printf("%lld",fin);
return 0;
}