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 Ruby (2.3.3) (judge verdict: Accepted)

require 'set'
lines = readlines.map{|line| line.split(' ').map(&:to_i)}
x=lines[0][0]
a=lines[1]
b=1
c=Set.new
for i in 0..x-1
  d=c.add?(a[i])
  if d==nil then
    b=0
    break
  end
end
if b==1 then
  puts 'YES'
else
  puts 'NO'
end