BZOJ 1231: [Usaco2008 Nov]mixup2 混乱的奶牛 状态压缩dp

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;
}