FIRS - Hàng cây
Tác giả: flashmt
Ngôn ngữ: Pascal
const fi='';
fo='';
maxn=100000;
var n,re,dem:longint;
a,b,d:array[1..maxn] of longint;
procedure rf;
var i:longint;
begin
assign(input,fi);
reset(input);
readln(n);
for i:=1 to n do
begin
read(a[i]);
b[i]:=i;
end;
close(input);
end;
procedure sort(l,r:longint);
var i,j,x,y,xx:longint;
begin
i:=l; j:=r; x:=a[(i+j) div 2]; xx:=b[(i+j) div 2];
repeat
while (a[i]<x) or ((a[i]=x) and (b[i]<xx)) do i:=i+1;
while (a[j]>x) or ((a[j]=x) and (b[j]>xx)) do j:=j-1;
if i<=j then
begin
y:=a[i]; a[i]:=a[j]; a[j]:=y;
y:=b[i]; b[i]:=b[j]; b[j]:=y;
i:=i+1; j:=j-1;
end;
until i>j;
if i<r then sort(i,r);
if l<j then sort(l,j);
end;
function check(x:longint):boolean;
begin
check:=(x>0) and (x<=n);
end;
procedure pr;
var cur,i:longint;
begin
sort(1,n);
fillchar(d,sizeof(d),0);
dem:=0; re:=0; cur:=1;
repeat
inc(re);
while d[b[cur]]=1 do inc(cur);
d[b[cur]]:=1; inc(dem);
for i:=0 to 1 do
if check(b[cur]-1+2*i) and (d[b[cur]-1+2*i]=0) then
begin
inc(dem); d[b[cur]-1+2*i]:=1;
end;
inc(cur);
until dem=n;
end;
procedure wf;
begin
assign(output,fo);
rewrite(output);
write(re);
close(output);
end;
begin
rf;
pr;
wf;
end.