bzoj4008

好题，这题可以分开算每个技能的贡献

orz popoqqq http://blog.csdn.net/popoqqq/article/details/45365759

 var f,w:array[..,..] of double;
     p:array[..] of double;
     d:array[..] of longint;
     t,i,j,n,m:longint;
     ans:double;
 
 begin
   readln(t);
   while t> do
   begin
     dec(t);
     readln(n,m);
     fillchar(f,sizeof(f),);
     for i:= to n do
       readln(p[i],d[i]);
     ans:=;
     for i:= to n do
     begin
       w[i,]:=;
       for j:= to m do
         w[i,j]:=w[i,j-]*(-p[i]);
     end;
     f[,m]:=;
     for i:= to n- do
       for j:= to m do
       begin
         f[i+,j]:=f[i+,j]+f[i,j]*w[i+,j];
         if j> then
         begin
           f[i+,j-]:=f[i+,j-]+f[i,j]*(-w[i+,j]);
           ans:=ans+f[i,j]*(-w[i+,j])*d[i+];
         end;
       end;
     writeln(ans::);
   end;
 end.