APIO2010特别行动队（单调队列、斜率优化）

其实这题一看知道应该是DP，再一看数据范围肯定就是单调队列了。

不过我还不太懂神马单调队列、斜率优化……

附上天牛的题解：http://www.cnblogs.com/neverforget/archive/2012/04/19/2456483.html

 var f,g:array[..] of int64;
     s,q:array[..] of longint;
     a,b,c,n,i,h,t,x:longint;
     bestk:double;
 procedure init;
  begin
  readln(n);
  readln(a,b,c);
  s[]:=;
  for i:= to n do
   begin
   read(x);
   s[i]:=s[i-]+x;
   end;
  end;
 function k(x,y:longint):double;
  begin
  exit(double(g[y]-g[x])/(s[y]-s[x]));
  end;
 procedure main;
  begin
  f[]:=;h:=;t:=;q[]:=;
  for i:= to n do
   begin
   bestk:=double(*a*s[i]);
   while (h<t) and (k(q[h],q[h+])>=bestk) do inc(h);
   f[i]:=int64(f[q[h]])+int64(a)*int64(s[i]-s[q[h]])*int64(s[i]-s[q[h]])
        +int64(b)*int64(s[i]-s[q[h]])+int64(c);
   g[i]:=int64(f[i])+int64(a)*int64(s[i])*int64(s[i])-int64(b)*int64(s[i]);
   while (h+<=t) and (k(q[t],i)>k(q[t-],q[t])) do dec(t);
   inc(t);
   q[t]:=i;
   end;
  end;
 procedure print;
  begin
  writeln(f[n]);
  end;
 begin
  init;
  main;
  print;
 end.