洛谷P2289 [HNOI2004]邮递员（插头dp）

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太神仙了……讲不来讲不来->这里

 //minamoto
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #define ll long long
 using namespace std;
 const int cube=1e9,mod=;
 int n,m;
 struct node{
     int bit[];
     inline void clear(){memset(bit,,sizeof(bit));}
     node(){clear();}
     inline void set(int t){clear();while(t)bit[++bit[]]=t%cube,t/=cube;}
     inline int &operator [](int x){return bit[x];}
     inline void print(){
         printf("%d",bit[bit[]]);
         for(int i=bit[]-;i;--i) printf("%09d",bit[i]);
         putchar();
     }
     inline node operator +(node b){
         node c;
         c[]=max(bit[],b[])+;
         for(int i=;i<=c[];++i)
         c[i]+=bit[i]+b[i],c[i+]+=c[i]/cube,c[i]%=cube;
         while(!c[c[]]) --c[];
         return c;
     }
     inline void operator +=(node b){*this=*this+b;}
     inline void operator =(int x){set(x);}
 }ans;
 struct Ha{
     node val[mod];
     int key[mod],sz,Hash[mod];
     inline void init(){
         memset(val,,sizeof(val)),memset(key,-,sizeof(key));
         sz=,memset(Hash,,sizeof(Hash));
     }
     inline void newhash(int id,int v){Hash[id]=++sz,key[sz]=v;}
     node &operator [](const int state){
         for(int i=state%mod;;i=(i+==mod)?:i+){
             if(!Hash[i]) newhash(i,state);
             if(key[Hash[i]]==state) return val[Hash[i]];
         }
     }
 }f[];
 inline int find(int state,int id){return (state>>((id-)<<))&;}
 inline void set(int &state,int bit,int val){bit=(bit-)<<,state|=<<bit,state^=<<bit,state|=val<<bit;}
 int link(int state,int pos){
     int cnt=,del=(find(state,pos)==)?:-;
     for(int i=pos;i&&i<=m+;i+=del){
         int plug=find(state,i);
         if(plug==) ++cnt;
         else if(plug==) --cnt;
         if(!cnt) return i;
     }
     return -;
 }
 void solve(int x,int y){
     int now=((x-)*m+y)&,last=now^,tot=f[last].sz;
     f[now].init();
     for(int i=;i<=tot;++i){
         int state=f[last].key[i];
         node val=f[last].val[i];
         int plug1=find(state,y),plug2=find(state,y+);
         if(link(state,y)==-||link(state,y+)==-) continue;
         if(!plug1&&!plug2){if(x!=n&&y!=m)set(state,y,),set(state,y+,),f[now][state]+=val;}
         else if(plug1&&!plug2){
             if(x!=n) f[now][state]+=val;
             if(y!=m) set(state,y,),set(state,y+,plug1),f[now][state]+=val;
         }
         else if(!plug1&&plug2){
             if(y!=m) f[now][state]+=val;
             if(x!=n)  set(state,y,plug2),set(state,y+,),f[now][state]+=val;
          }
          else if(plug1==&&plug2==)
          set(state,link(state,y+),),set(state,y,),set(state,y+,),f[now][state]+=val;
          else if(plug1==&&plug2==){if(x==n&&y==m)ans+=val;}
          else if(plug1==&&plug2==)set(state,y,),set(state,y+,),f[now][state]+=val;
          else if(plug1==&&plug2==)
          set(state,link(state,y),),set(state,y,),set(state,y+,),f[now][state]+=val;
     }
 }
 int main(){
 //    freopen("testdata.in","r",stdin);
     scanf("%d%d",&n,&m);
     if(n==||m==) return puts(""),;
     if(m>n) swap(n,m);
     f[].init(),f[][]=;
     for(int i=;i<=n;++i){
         for(int j=;j<=m;++j) solve(i,j);
         if(i!=n){
             int now=(i*m)&,tot=f[now].sz;
             for(int j=;j<=tot;++j)
             f[now].key[j]<<=;
         }
     }
     ans+=ans,ans.print();
     return ;
 }