POJ 1830（位运算+双向DFS）

此题也可用GE做，可是我不会矩阵乘法……

Program P1830;const   maxn=28;   maxf=100007;   none=-2139062144;var   ans,tt,n,i,j,s,t,mid:longint;   b:array[1..29] of longint;   h,num:array[0..maxf] of longint;function hash(x:longint):longint;var   i,j:longint;begin   hash:=x mod maxf;   while (num[hash]<>x) and (num[hash]<>none) do   begin      hash:=(hash+1) mod maxf;   end;   num[hash]:=x;   exit(hash);end;procedure dfs(x,l:longint);var   i,j:longint;begin   if l=mid+1 then   begin      inc(h[hash(x)]);      exit;   end;   for i:=l to mid do      dfs(x xor b[i],i+1);   dfs(x,mid+1);end;procedure find(x,l:longint);var   i,j:longint;begin   if l=n+1 then   begin      inc(ans,h[hash(x)]);      exit;   end;   for i:=l to n do      find(x xor b[i],i+1);   find(x,n+1);end;begin   read(tt);   while (tt>0) do   begin      ans:=0;      fillchar(b,sizeof(b),0);      fillchar(num,sizeof(num),128);      fillchar(h,sizeof(h),0);      read(n);      s:=0;      for i:=1 to n do      begin         read(j);         if j=1 then inc(s,1 shl (i-1));      end;      t:=0;      for i:=1 to n do      begin         read(j);         if j=1 then inc(t,1 shl (i-1));      end;      while (true) do      begin         read(i,j);         if (i=0) and (j=0) then break;         inc(b[i],1 shl (j-1));      end;      for i:=1 to n do inc(b[i],1 shl (i-1));      mid:=n shr 1;      dfs(s,1);      find(t,mid+1);      if ans=0 then writeln('Oh,it''s impossible~!!') else      writeln(ans);      dec(tt);   end;end.