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.

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