HNOI2008玩具装箱 （斜率优化）

总算A了，心情好激动……

如果会了一类斜率优化，基本上这类题就成了套模版了……

只是k函数不同

 var n,l,x,tail,head,m:int64;
     i,j:longint;
     dp,q,s:array[..] of int64;
 function k(x,y:longint):double;
  begin
  k:=1.0*((dp[x]+s[x]*s[x]-dp[y]-s[y]*s[y])/(s[x]-s[y]));
  end;
 procedure main;
  begin
  readln(n,l);s[]:=;
  for i:= to n do
   begin
   readln(x);
   s[i]:=s[i-]+x;
   end;
  for i:= to n do s[i]:=s[i]+i;
  head:=;tail:=;
  for i:= to n do
   begin
   m:=s[i]-l-;
   while (head<tail) and (k(q[head+],q[head])<=*m) do inc(head);
   j:=q[head];
   dp[i]:=dp[j]+(m-s[j])*(m-s[j]);
   while (head<tail) and (k(q[tail],q[tail-])>=k(i,q[tail])) do dec(tail);
   inc(tail);q[tail]:=i;
   end;
  writeln(dp[n]);
  end;
 begin
  main;
 end.        

还有一份写得很不错的题解：

http://www.cnblogs.com/perseawe/archive/2012/05/12/BZ1010.html