LeetCode-in-Java

3508. Implement Router

Medium

Design a data structure that can efficiently manage data packets in a network router. Each data packet consists of the following attributes:

source: A unique identifier for the machine that generated the packet.
destination: A unique identifier for the target machine.
timestamp: The time at which the packet arrived at the router.

Implement the Router class:

Router(int memoryLimit): Initializes the Router object with a fixed memory limit.

memoryLimit is the maximum number of packets the router can store at any given time.
If adding a new packet would exceed this limit, the oldest packet must be removed to free up space.

bool addPacket(int source, int destination, int timestamp): Adds a packet with the given attributes to the router.

A packet is considered a duplicate if another packet with the same source, destination, and timestamp already exists in the router.
Return true if the packet is successfully added (i.e., it is not a duplicate); otherwise return false.

int[] forwardPacket(): Forwards the next packet in FIFO (First In First Out) order.

Remove the packet from storage.
Return the packet as an array [source, destination, timestamp].
If there are no packets to forward, return an empty array.

int getCount(int destination, int startTime, int endTime):

Returns the number of packets currently stored in the router (i.e., not yet forwarded) that have the specified destination and have timestamps in the inclusive range [startTime, endTime].

Note that queries for addPacket will be made in increasing order of timestamp.

Example 1:

Input:
[“Router”, “addPacket”, “addPacket”, “addPacket”, “addPacket”, “addPacket”, “forwardPacket”, “addPacket”, “getCount”]
[[3], [1, 4, 90], [2, 5, 90], [1, 4, 90], [3, 5, 95], [4, 5, 105], [], [5, 2, 110], [5, 100, 110]]

Output:
[null, true, true, false, true, true, [2, 5, 90], true, 1]

Explanation

Router router = new Router(3); // Initialize Router with memoryLimit of 3.
router.addPacket(1, 4, 90); // Packet is added. Return True.
router.addPacket(2, 5, 90); // Packet is added. Return True.
router.addPacket(1, 4, 90); // This is a duplicate packet. Return False.
router.addPacket(3, 5, 95); // Packet is added. Return True
router.addPacket(4, 5, 105); // Packet is added, [1, 4, 90] is removed as number of packets exceeds memoryLimit. Return True.
router.forwardPacket(); // Return [2, 5, 90] and remove it from router.
router.addPacket(5, 2, 110); // Packet is added. Return True.
router.getCount(5, 100, 110); // The only packet with destination 5 and timestamp in the inclusive range [100, 110] is [4, 5, 105]. Return 1.

Example 2:

Input:
[“Router”, “addPacket”, “forwardPacket”, “forwardPacket”]
[[2], [7, 4, 90], [], []]

Output:
[null, true, [7, 4, 90], []]

Explanation

Router router = new Router(2); // Initialize Router with memoryLimit of 2.
router.addPacket(7, 4, 90); // Return True.
router.forwardPacket(); // Return [7, 4, 90].
router.forwardPacket(); // There are no packets left, return [].

Constraints:

2 <= memoryLimit <= 10⁵
1 <= source, destination <= 2 * 10⁵
1 <= timestamp <= 10⁹
1 <= startTime <= endTime <= 10⁹
At most 10⁵ calls will be made to addPacket, forwardPacket, and getCount methods altogether.
queries for addPacket will be made in increasing order of timestamp.

Solution

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Queue;

@SuppressWarnings("java:S135")
public class Router {
    private final int size;
    private int cur;
    private final Queue<int[]> q;
    private final HashMap<Integer, ArrayList<int[]>> map;

    public Router(int memoryLimit) {
        q = new LinkedList<>();
        map = new HashMap<>();
        size = memoryLimit;
        cur = 0;
    }

    public boolean addPacket(int source, int destination, int timestamp) {
        if (map.containsKey(destination)) {
            boolean found = false;
            ArrayList<int[]> list = map.get(destination);
            for (int i = list.size() - 1; i >= 0; i--) {
                if (list.get(i)[1] < timestamp) {
                    break;
                } else if (list.get(i)[0] == source) {
                    found = true;
                    break;
                }
            }
            if (found) {
                return false;
            }
        }
        if (map.containsKey(destination)) {
            ArrayList<int[]> list = map.get(destination);
            list.add(new int[] {source, timestamp});
            cur++;
            q.offer(new int[] {source, destination, timestamp});
        } else {
            ArrayList<int[]> temp = new ArrayList<>();
            temp.add(new int[] {source, timestamp});
            cur++;
            map.put(destination, temp);
            q.offer(new int[] {source, destination, timestamp});
        }
        if (cur > size) {
            forwardPacket();
        }
        return true;
    }

    public int[] forwardPacket() {
        if (q.isEmpty()) {
            return new int[] {};
        }
        int[] temp = q.poll();
        ArrayList<int[]> list = map.get(temp[1]);
        list.remove(0);
        if (list.isEmpty()) {
            map.remove(temp[1]);
        }
        cur--;
        return temp;
    }

    public int getCount(int destination, int startTime, int endTime) {
        if (map.containsKey(destination)) {
            ArrayList<int[]> list = map.get(destination);
            int lower = -1;
            int higher = -1;
            for (int i = 0; i < list.size(); i++) {
                if (list.get(i)[1] >= startTime) {
                    lower = i;
                    break;
                }
            }
            for (int i = list.size() - 1; i >= 0; i--) {
                if (list.get(i)[1] <= endTime) {
                    higher = i;
                    break;
                }
            }
            if (lower == -1 || higher == -1) {
                return 0;
            } else {
                return Math.max(0, higher - lower + 1);
            }
        } else {
            return 0;
        }
    }
}

/*
 * Your Router object will be instantiated and called as such:
 * Router obj = new Router(memoryLimit);
 * boolean param_1 = obj.addPacket(source,destination,timestamp);
 * int[] param_2 = obj.forwardPacket();
 * int param_3 = obj.getCount(destination,startTime,endTime);
 */

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