SPSEQ - Sequences
Tác giả: RR
Ngôn ngữ: Pascal
//Written by RR
{$MODE OBJFPC}
uses math;
const
FINP = '';
FOUT = '';
MAXN = 100111;
var
f1,f2 : text;
n,s : longint;
a,ind,c : array[1..MAXN] of longint;
f,g : array[1..MAXN] of longint;
ln : array[1..MAXN] of longint;
procedure openF;
begin
assign(f1,FINP); reset(f1);
assign(f2,FOUT); rewrite(f2);
end;
procedure closeF;
begin
close(f1);
close(f2);
end;
procedure inp;
var
i:longint;
begin
read(f1,n);
for i:=1 to n do
read(f1,a[i]);
end;
procedure swap(var a,b:longint);
var
tmp:longint;
begin
tmp:=a; a:=b; b:=tmp;
end;
procedure sort(l,r:longint);
var
i,j,mid:longint;
begin
i:=l; j:=r; mid:=c[l+random(r-l+1)];
repeat
while c[i]<mid do inc(i);
while c[j]>mid do dec(j);
if i<=j then
begin
swap(c[i],c[j]);
swap(ind[i],ind[j]);
inc(i); dec(j);
end;
until i>j;
if i<r then sort(i,r);
if l<J then sort(l,j);
end;
procedure RR;
var
i:longint;
begin
for i:=1 to n do
begin
c[i]:=a[i];
ind[i]:=i;
end;
sort(1,n);
a[ind[1]]:=1; s:=1;
for i:=2 to n do
begin
if c[i]>c[s] then
begin
inc(s);
c[s]:=c[i];
end;
a[ind[i]]:=s;
end;
end;
function get(u:longint):longint;
var
v:longint;
begin
if (u<=0) then exit(0);
v:=u-u and (-u);
exit(max(ln[u],get(v)));
end;
procedure update(u,k:longint);
var
v:longint;
begin
ln[u]:=max(ln[u],k);
v:=u+u and (-u);
if v<=s then update(v,k);
end;
procedure solve;
var
i,res:longint;
begin
for i:=1 to n do
begin
f[i]:=get(a[i]-1)+1;
update(a[i],f[i]);
end;
fillchar(ln,sizeof(ln),0);
for i:=n downto 1 do
begin
g[i]:=get(a[i]-1)+1;
update(a[i],g[i]);
end;
res:=0;
for i:=1 to n do
res:=max(res,min(f[i],g[i])*2-1);
writeln(f2,res);
end;
begin
openF;
inp;
RR;
solve;
closeF;
end.