传送门

完了……好像……已经把插头dp全都忘光了……
可以去看看这篇blog
为了卡常变得丧心病狂的代码

//minamoto
#include<bits/stdc++.h>
#define ll long long
#define R register
#define fp(i,a,b) for(R int i=a,I=b+1;i<I;++i)
#define fd(i,a,b) for(R int i=a,I=b-1;i>I;--i)
#define go(u) for(int i=head[u],v=e[i].v;i;i=e[i].nx,v=e[i].v)
using namespace std;
const int N=25,P=23333,M=40005;
struct MAIN{int n,m;char s[N];bool mp[N][N];int cnt[2],cur,vis[2][M],hsh[P+5],ex,ey,S,l,r,dt,val;ll dp[2][M],ans;void insert(R int S,R ll sum){R int pos=S%P;while(hsh[pos]){if(vis[cur][hsh[pos]]==S)return (void)(dp[cur][hsh[pos]]+=sum);pos=(pos+1)%P;}hsh[pos]=++cnt[cur],vis[cur][hsh[pos]]=S,dp[cur][hsh[pos]]=sum;}MAIN(){scanf("%d%d",&n,&m);fp(i,1,n){scanf("%s",s+1);fp(j,1,m)if(s[j]=='.')mp[i][j]=1,ex=i,ey=j;}dp[0][1]=cnt[0]=1;fp(i,1,n){fp(j,1,m){cnt[cur^=1]=0;memset(hsh,0,sizeof(hsh));fp(k,1,cnt[cur^1]){S=vis[cur^1][k],l=(S>>((j-1)<<1))&3,r=(S>>(j<<1))&3;if(!mp[i][j]){if(!l&&!r)insert(S,dp[cur^1][k]);continue;}if(!l&&!r){if(!mp[i][j+1]||!mp[i+1][j])continue;insert(S^(1<<((j-1)<<1))^(2<<(j<<1)),dp[cur^1][k]);}if(l&&!r){if(mp[i][j+1])insert(S^(l<<((j-1)<<1))^(l<<(j<<1)),dp[cur^1][k]);if(mp[i+1][j])insert(S,dp[cur^1][k]);}if(!l&&r){if(mp[i+1][j])insert(S^(r<<(j<<1))^(r<<((j-1)<<1)),dp[cur^1][k]);if(mp[i][j+1])insert(S,dp[cur^1][k]);}if(l==1&&r==1){dt=1;fp(p,j+1,m){val=(S>>(p<<1))&3;if(val==1)++dt;if(val==2)--dt;if(!dt){S^=(2<<(p<<1))^(1<<(p<<1));break;}}insert(S^(1<<((j-1)<<1))^(1<<(j<<1)),dp[cur^1][k]);}if(l==2&&r==2){dt=1;fd(p,j-2,0){val=(S>>(p<<1))&3;if(val==1)--dt;if(val==2)++dt;if(!dt){S^=(1<<(p<<1))^(2<<(p<<1));break;}}insert(S^(2<<((j-1)<<1))^(2<<(j<<1)),dp[cur^1][k]);}if(l==2&&r==1)insert(S^(2<<((j-1)<<1))^(1<<(j<<1)),dp[cur^1][k]);if(l==1&&r==2&&i==ex&&j==ey)ans+=dp[cur^1][k];}}fp(j,1,cnt[cur])vis[cur][j]<<=2;}printf("%lld\n",ans);}
}T;
int main(){return 0;}