洛谷 2915 [USACO08NOV]奶牛混合起来Mixed Up Cows

一道水状压，然而不知道是不是太久没做过dp了，我盯着它二十分钟才反应过来。。。。

还把数组开小了WA了一发QAQ

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//Twenty #include<algorithm> #include<iostream> #include<cstring> #include<cstdlib> #include<cstdio> #include<vector> #include<cmath> #include<queue> #include<ctime> const int maxn=(1<<16)+2; typedef long long LL; using namespace std; int n,kk,nn,cnt[maxn],id[17]; LL dp[2][maxn][16];   namespace fastIO {     const int sz=1<<15|1;     char ch,buf[sz],*l,*r;     void gechar(char &c) {         if(l==r) r=(l=buf)+fread(buf,1,sz,stdin);         c = l==r?(char)EOF:*l++;     }     template<typename T> void read(T &x) {         int f=1; x=0; gechar(ch);         while(ch!='-'&&(ch<'0'||ch>'9')) gechar(ch);         if(ch=='-') f=-1,gechar(ch);         for(;ch>='0'&&ch<='9';gechar(ch)) x=x*10+ch-'0'; x*=f;     } }   void pre() {     nn=(1<<n)-1;     for(int i=0;i<=nn;i++) {         int tp=i;         while(tp) {             cnt[i]++;             tp-=(tp&(-tp));         }     } }   void work() {     int o=0;     dp[o][0][0]=1;     id[0]=1e9;     LL ans=0;     for(int i=1;i<=n;i++) {         o^=1;         for(int j=1;j<=nn;j++) if(cnt[j]==i) {             for(int k=1;k<=n;k++) {                 int fl=0;                 if(j&(1<<k-1)) {                     int pr=j^(1<<k-1);                     for(int l=(i!=1);l<=n;l++)                         if(dp[o^1][pr][l]&&abs(id[l]-id[k])>kk) {                         if(fl==0) {                             dp[o][j][k]=dp[o^1][pr][l];                             fl=1;                         }                         else dp[o][j][k]+=dp[o^1][pr][l];                     }                   }                 if(!fl) dp[o][j][k]=0;                 if(i==n)                     ans+=dp[o][j][k];             }         }     }     printf("%lld\n",ans); }   void init() {     fastIO::read(n);     fastIO::read(kk);     for(int i=1;i<=n;i++) fastIO::read(id[i]); }   //#define DEBUG int main()  { #ifdef DEBUG     freopen("1.in","r",stdin);     //freopen(".out","w",stdout); #endif     init();     pre();     work();     return 0; }