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easyArrays & Hashing+10 XPTime limit 2s

Given an array of integers, decide whether any value appears at least twice.

Input:

line 1: n
line 2: n integers

Output: true if some value repeats, otherwise false.

Constraints: 1 ≤ n ≤ 10⁵, −10⁹ ≤ a[i] ≤ 10⁹.

Think about it: comparing every pair is O(n²) — too slow for 10⁵ numbers. Can a set remember what you have already seen?

Sample input 1

4
1 2 3 1

Sample output 1

true

Sample input 2

4
1 2 3 4

Sample output 2

false

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