fn sales_by_match(n: i32, ar: &[i32]) -> i32 {
    //Time complexity: O(n)
    //Space complexity (ignoring input): O(n)
    let mut socks_hash = std::collections::HashMap::new();
    for sock in ar {
        match socks_hash.get(sock) {
            Some(v) => socks_hash.insert(sock, v + 1),
            None => socks_hash.insert(sock, 1),
        };
    }
    let mut total_pairs = 0;
    for values in socks_hash.values() {
        total_pairs += values / 2;
    }
    total_pairs
}