# Sales Rank

# A large eCommerce company wishes to list the best-selling products, overall and by category.
# For example, one product might be the #1056th best-selling product overall but the 13th
    # best-selling product under "Sports Equipment" and the #24th best-selling product under
    # "Safety".
    
# Describe how you would design this system.

# time complexity:  O()
# space complexity:  O()