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[0..100000] 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[0]:=0;
 for i:=1 to n do
  begin
  readln(x);
  s[i]:=s[i-1]+x;
  end;
 for i:=1 to n do s[i]:=s[i]+i;
 head:=0;tail:=0;
 for i:=1 to n do
  begin
  m:=s[i]-l-1;
  while (head<tail) and (k(q[head+1],q[head])<=2*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-1])>=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