开始读错题了，然后发现一眼切~
Code:
#include <cstdio>
#include <algorithm>
#define ll long long
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int s[20];
ll dp[1<<18][17],fac[20];
int main() {
// setIO("input");
int n,k,i,j,l;
scanf("%d%d",&n,&k);
fac[0]=1;
for(i=1;i<=n;++i) fac[i]=fac[i-1]*i;
for(i=0;i<n;++i) scanf("%d",&s[i]), dp[(1<<i)][i]=1;
for(l=1;l<(1<<n);++l) {
for(j=0;(1<<j)<=l;++j) {
if((l&(1<<j)) && dp[l][j]) {
for(int p=0;(1<<p)<(1<<n);++p) {
if(((1<<p)^l)&&abs(s[p]-s[j])>k){
dp[l^(1<<p)][p]+=dp[l][j];
}
}
}
}
}
ll re=0;
for(i=0;i<n;++i) re+=dp[(1<<n)-1][i];
printf("%lld\n",re);
return 0;
}
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