bzoj3437

练一下斜率优化

var s1,s2,f:array[0..1000010] of int64;
    q,a,b:array[0..1000010] of longint;
    i,n,h,t,j:longint;

function g(j,k:longint):double;
  var a,b:double;
  begin
    a:=f[j]-f[k]-s2[j]+s2[k];
    b:=s1[k]-s1[j];
    exit(a/b);
  end;

begin
  readln(n);
  for i:=1 to n do
    read(a[i]);
  for i:=1 to n do
  begin
    read(b[i]);
    s1[i]:=s1[i-1]+b[i];
    s2[i]:=s2[i-1]+int64(b[i])*int64(n-i+1);
  end;
  h:=0;
  t:=0;
  for i:=1 to n do
  begin
    while (h<t) and (g(q[h],q[h+1])>=n-i+1) do inc(h);
    j:=q[h];
    f[i]:=f[j]+a[i]+s2[i-1]-s2[j]-(s1[i-1]-s1[j])*int64(n-i+1);
    while (h<t) and (g(q[t],i)>=g(q[t-1],q[t])) do dec(t);
    inc(t);
    q[t]:=i;
  end;
  writeln(f[n]);
end.