LeetCode 1532: The Most Recent Three Orders Solution

Master LeetCode problem 1532 (The Most Recent Three Orders), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1532. The Most Recent Three Orders

Medium

Database

Problem Explanation

Explanation:

To solve this problem, we can maintain a data structure to store the most recent three orders for each customer. We can use a HashMap where the key is the customer id and the value is a Queue of the most recent three orders. Whenever a new order comes in for a customer, we update the Queue with the latest order and remove the oldest one if necessary.

Algorithmic Idea:

Initialize a HashMap to store the most recent three orders for each customer.
For each new order:
- Check if the customer already exists in the HashMap.
- If the customer exists:
  - Update the existing Queue with the new order and remove the oldest order if the Queue size exceeds three.
- If the customer does not exist:
  - Create a new Queue with the new order and add it to the HashMap.

Time Complexity:

Inserting a new order: O(1)
Removing the oldest order if the Queue size exceeds three: O(1)

Space Complexity:

O(n) where n is the number of unique customers.

Solution Code

class RecentOrders {
    Map<Integer, Queue<Integer>> recentOrders;

    public RecentOrders() {
        recentOrders = new HashMap<>();
    }

    public void addOrder(int customer_id, int order_id) {
        if (recentOrders.containsKey(customer_id)) {
            Queue<Integer> queue = recentOrders.get(customer_id);
            queue.offer(order_id);
            if (queue.size() > 3) {
                queue.poll();
            }
        } else {
            Queue<Integer> queue = new LinkedList<>();
            queue.offer(order_id);
            recentOrders.put(customer_id, queue);
        }
    }

    public List<Integer> getRecentOrders(int customer_id) {
        if (recentOrders.containsKey(customer_id)) {
            return new ArrayList<>(recentOrders.get(customer_id));
        } else {
            return new ArrayList<>();
        }
    }
}

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