Problem:
Score : 300 points

Problem Statement

Given is a sequence of integers A_1, A_2, ..., A_N.
If its elements are pairwise distinct, print YES; otherwise, print NO.

Constraints

2 ≤ N ≤ 200000

1 ≤ A_i ≤ 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 ... A_N

Output

If the elements of the sequence are pairwise distinct, print YES; otherwise, print NO.

Sample Input 1

5
2 6 1 4 5

Sample Output 1

YES

The elements are pairwise distinct.

Sample Input 2

6
4 1 3 1 6 2

Sample Output 2

NO

The second and fourth elements are identical.

Sample Input 3

2
10000000 10000000

Sample Output 3

NO

Solution in Pascal (FPC 2.6.2) (judge verdict: Accepted)

var n,i,t,p:longint;
    res,ord:array[0..1000000]of longword;
    a,b:array[0..1000000]of word;
    cnt:array[0..65535]of longint;
begin
  readln(n);
  for i:=1 to n do
  begin
    read(t);
    a[i]:=t>>16;
    b[i]:=t and pred(1<<16);
    inc(cnt[b[i]]);
  end;
  p:=1;
  for i:=0 to 65534 do
  begin
    inc(cnt[p],cnt[i]);
    inc(p);
  end;
  for i:=1 to n do
  begin
    ord[cnt[b[i]]]:=i;
    dec(cnt[b[i]]);
  end;
  fillchar(cnt,sizeof(cnt),0);
  for i:=1 to n do
    inc(cnt[a[i]]);
  p:=1;
  for i:=0 to 65534 do
  begin
    inc(cnt[p],cnt[i]);
    inc(p);
  end;
  for i:=n downto 1 do
  begin
    p:=a[ord[i]];
    res[cnt[p]]:=ord[i];
    dec(cnt[p]);
  end;
  for i:=1 to n-1 do
    if a[res[i]]<<16 or b[res[i]]=a[res[i+1]]<<16 or b[res[i+1]] then
    begin
      writeln('NO');
      halt;
    end;
  writeln('YES');
end.