LeetCode-in-Java

3815. Design Auction System

Medium

You are asked to design an auction system that manages bids from multiple users in real time.

Each bid is associated with a userId, an itemId, and a bidAmount.

Implement the AuctionSystem class:

• AuctionSystem(): Initializes the AuctionSystem object.
• void addBid(int userId, int itemId, int bidAmount): Adds a new bid for itemId by userId with bidAmount. If the same userId already has a bid on itemId, replace it with the new bidAmount.
• void updateBid(int userId, int itemId, int newAmount): Updates the existing bid of userId for itemId to newAmount. It is guaranteed that this bid exists.
• void removeBid(int userId, int itemId): Removes the bid of userId for itemId. It is guaranteed that this bid exists.
• int getHighestBidder(int itemId): Returns the userId of the highest bidder for itemId. If multiple users have the same highest bidAmount, return the user with the highest userId. If no bids exist for the item, return -1.

Example 1:

Input:
[“AuctionSystem”, “addBid”, “addBid”, “getHighestBidder”, “updateBid”, “getHighestBidder”, “removeBid”, “getHighestBidder”, “getHighestBidder”]
[[], [1, 7, 5], [2, 7, 6], [7], [1, 7, 8], [7], [2, 7], [7], [3]]

Output:
[null, null, null, 2, null, 1, null, 1, -1]

Explanation

AuctionSystem auctionSystem = new AuctionSystem(); // Initialize the Auction system
auctionSystem.addBid(1, 7, 5); // User 1 bids 5 on item 7
auctionSystem.addBid(2, 7, 6); // User 2 bids 6 on item 7
auctionSystem.getHighestBidder(7); // return 2 as User 2 has the highest bid
auctionSystem.updateBid(1, 7, 8); // User 1 updates bid to 8 on item 7
auctionSystem.getHighestBidder(7); // return 1 as User 1 now has the highest bid
auctionSystem.removeBid(2, 7); // Remove User 2’s bid on item 7
auctionSystem.getHighestBidder(7); // return 1 as User 1 is the current highest bidder
auctionSystem.getHighestBidder(3); // return -1 as no bids exist for item 3

Constraints:

• 1 <= userId, itemId <= 5 * 104
• 1 <= bidAmount, newAmount <= 109
• At most 5 * 104 total calls to addBid, updateBid, removeBid, and getHighestBidder.
• The input is generated such that for updateBid and removeBid, the bid from the given userId for the given itemId will be valid.

Solution

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.PriorityQueue;

public class AuctionSystem {
    private final Map<Long, int[]> bidMap;
    private final Map<Integer, PriorityQueue<int[]>> itemMap;

    public AuctionSystem() {
        bidMap = new HashMap<>();
        itemMap = new HashMap<>();
    }

    public void addBid(int userId, int itemId, int bidAmount) {
        int[] bid = new int[] {userId, itemId, bidAmount};
        bidMap.put((long) userId << 32 | itemId, bid);
        itemMap.computeIfAbsent(
                        itemId,
                        item ->
                                new PriorityQueue<>(
                                        (a, b) -> a[2] == b[2] ? b[0] - a[0] : b[2] - a[2]))
                .add(bid);
    }

    public void updateBid(int userId, int itemId, int newAmount) {
        addBid(userId, itemId, newAmount);
    }

    public void removeBid(int userId, int itemId) {
        bidMap.remove((long) userId << 32 | itemId);
    }

    public int getHighestBidder(int itemId) {
        PriorityQueue<int[]> pq = itemMap.get(itemId);
        if (pq == null || pq.isEmpty()) {
            return -1;
        }
        while (!pq.isEmpty()) {
            int[] top = pq.peek();
            int[] cur = bidMap.get((long) top[0] << 32 | itemId);
            if (Arrays.equals(top, cur)) {
                return top[0];
            }
            pq.poll();
        }
        return -1;
    }
}

/**
 * Your AuctionSystem object will be instantiated and called as such: AuctionSystem obj = new
 * AuctionSystem(); obj.addBid(userId,itemId,bidAmount); obj.updateBid(userId,itemId,newAmount);
 * obj.removeBid(userId,itemId); int param_4 = obj.getHighestBidder(itemId);
 */

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