Apply a flash sale price cap to a cart

During a flash sale, no item in a cart can cost more than a set maximum. The checkout applies that cap to each item before it adds up the total.

Write cap_prices(prices, cap) that returns the cart's prices after the cap.

Input and output:

• prices: a list of up to 100,000 prices in cents, each an integer between 0 and 1,000,000. It may be empty.
• cap: the maximum price in cents, an integer between 0 and 1,000,000.
• Returns a list of integers, one per item, in the same order as prices.

Rules:

• A price above cap becomes exactly cap.
• A price at or below cap stays as it is.
• You may change prices in place and return it, or return a new list.