LeetCode in Kotlin

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.PriorityQueue

class AuctionSystem {
    private val bidMap: MutableMap<Long?, IntArray?> = HashMap<Long?, IntArray?>()
    private val itemMap: MutableMap<Int?, PriorityQueue<IntArray>?> = HashMap<Int?, PriorityQueue<IntArray>?>()

    fun addBid(userId: Int, itemId: Int, bidAmount: Int) {
        val bid = intArrayOf(userId, itemId, bidAmount)
        bidMap[userId.toLong() shl 32 or itemId.toLong()] = bid
        itemMap.computeIfAbsent(
            itemId,
        ) {
            java.util.PriorityQueue<kotlin.IntArray>(
                java.util.Comparator { a: kotlin.IntArray, b: kotlin.IntArray ->
                    if (a[2] ==
                        b[2]
                    ) {
                        b[0] - a[0]
                    } else {
                        b[2] - a[2]
                    }
                },
            )
        }!!
            .add(bid)
    }

    fun updateBid(userId: Int, itemId: Int, newAmount: Int) {
        addBid(userId, itemId, newAmount)
    }

    fun removeBid(userId: Int, itemId: Int) {
        bidMap.remove(userId.toLong() shl 32 or itemId.toLong())
    }

    fun getHighestBidder(itemId: Int): Int {
        val pq = itemMap[itemId]
        if (pq.isNullOrEmpty()) {
            return -1
        }
        while (pq.isNotEmpty()) {
            val top = pq.peek()
            val cur = bidMap[top[0].toLong() shl 32 or itemId.toLong()]
            if (top.contentEquals(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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