Unique Transaction Pairs

You are tasked with analyzing transaction data for unique pairs of users who have completed transactions with the same amount. Given a list of transactions represented as integers, find how many unique user pairs (i, j) exist such that the transaction amounts are the same for both users, and i != j. Input: The first line contains an integer n (1 <= n <= 100,000), the number of transactions. The second line contains n space-separated integers representing the transaction amounts. Output: Print a single integer representing the number of unique pairs of users. Example: Input: 5 100 200 100 300 200 Output: 3