HYSBZ 1079(着色方案）

Dp 神奇的状态转移……

Program fd;const   mo=1000000007;var   n,i,j:longint;   c,tot:array[1..15] of longint;   f:array[0..15,0..15,0..15,0..15,0..15,0..15] of int64;function dfs(a1,a2,a3,a4,a5,last:longint):int64;var   i,j:longint;   ans,q:int64;   a:array[1..5] of longint;begin   if f[a1,a2,a3,a4,a5,last]>0 then exit(f[a1,a2,a3,a4,a5,last]);   a[1]:=a1;a[2]:=a2;a[3]:=a3;a[4]:=a4;a[5]:=a5;   ans:=0;   for i:=1 to 5 do      if (a[i]>0) then      begin         if (last=i+1) and (a[i]=1) then continue;  //     if (last=i+1) then dec(a[i]);         dec(a[i]);         if i>1 then inc(a[i-1]);         q:=dfs(a[1],a[2],a[3],a[4],a[5],i);         inc(a[i]);         if i>1 then dec(a[i-1]);         if last=i+1 then ans:=(ans+(a[i]-1)*q) mod mo         else ans:=(ans+a[i]*q) mod mo;  //     if (last=i+1) then inc(a[i]);      end;   f[a1,a2,a3,a4,a5,last]:=ans;   exit(ans);end;begin   read(n);   fillchar(tot,sizeof(tot),0);   for i:=1 to n do   begin      read(c[i]);      inc(tot[c[i]]);   end;   fillchar(f,sizeof(f),0);   for i:=1 to n do f[0,0,0,0,0,i]:=1;   writeln(dfs(tot[1],tot[2],tot[3],tot[4],tot[5],0));end.