A True Permutation

Difficulty: 1000 3500 ms 128 MB

implementation

Does the array contain each of 1, 2, ..., N exactly once?

Input: the first line has N; the second line has N integers.

Output: YES or NO.

Constraints:

• 1 ≤ N ≤ 10⁵
• |a_i| ≤ 10⁹

Sample Tests

4
2 4 1 3

YES

3
1 1 3

NO

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