Equal Pairs

Difficulty: 1000 3500 ms 128 MB

implementation

Count the pairs i < j with a_i = a_j.

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

Output: the number of equal-valued pairs.

Constraints:

• 1 ≤ N ≤ 10⁵
• |a_i| ≤ 10⁹

Sample Tests

5
1 2 1 1 2

4

2
3 4

0

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