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

 1 var n,l,x,tail,head,m:int64;

 2     i,j:longint;

 3     dp,q,s:array[0..100000] of int64;

 4 function k(x,y:longint):double;

 5  begin

 6  k:=1.0*((dp[x]+s[x]*s[x]-dp[y]-s[y]*s[y])/(s[x]-s[y]));

 7  end;

 8 procedure main;

 9  begin

10  readln(n,l);s[0]:=0;

11  for i:=1 to n do

12   begin

13   readln(x);

14   s[i]:=s[i-1]+x;

15   end;

16  for i:=1 to n do s[i]:=s[i]+i;

17  head:=0;tail:=0;

18  for i:=1 to n do

19   begin

20   m:=s[i]-l-1;

21   while (head<tail) and (k(q[head+1],q[head])<=2*m) do inc(head);

22   j:=q[head];

23   dp[i]:=dp[j]+(m-s[j])*(m-s[j]);

24   while (head<tail) and (k(q[tail],q[tail-1])>=k(i,q[tail])) do dec(tail);

25   inc(tail);q[tail]:=i;

26   end;

27  writeln(dp[n]);

28  end;

29 begin

30  main;

31 end.        

还有一份写得很不错的题解：

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

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