HNOI2008玩具装箱 （斜率优化）

 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.