bzoj3437

练一下斜率优化

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