2025-09-20 Daily Challenge

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In: DailyChallenge

Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 20

Description

Implement Router

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

class Router {
  int capacity;
  queue<long long> q;
  set<long long> packets;
  map<int, vector<int>> dest2packets;
  const long long BASE = 3e5;
  const long long ROUTEBASE = 1 << 20;
  constexpr long long getId(int source, int destination, int timestamp) {
    return (source * BASE + destination) * ROUTEBASE + timestamp;
  }
  vector<int> getFront() {
    long long id = q.front();
    return {int(id / ROUTEBASE / BASE), int(id / ROUTEBASE % BASE), int(id % ROUTEBASE)};
  }

  void popFront() {
    long long id = q.front();
    int dest = id / ROUTEBASE % BASE;
    q.pop();
    packets.erase(id);
    dest2packets[dest].erase(dest2packets[dest].begin());
  }
public:
  Router(int memoryLimit): capacity(memoryLimit) { }
  
  bool addPacket(int source, int destination, int timestamp) {
    long long id = getId(source, destination, timestamp);
    if(packets.count(id)) return false;
    if(q.size() == capacity) popFront();
    q.push(id);
    packets.insert(id);
    dest2packets[destination].push_back(timestamp);
    return true;
  }
  
  vector<int> forwardPacket() {
    if(q.empty()) return {};
    auto packet = getFront();
    popFront();
    return packet;
  }
  
  int getCount(int destination, int startTime, int endTime) {
    if(!dest2packets.count(destination)) return 0;
    auto &container = dest2packets[destination];
    auto begin = lower_bound(container.begin(), container.end(), startTime) - container.begin();
    auto end = upper_bound(container.begin(), container.end(), endTime) - container.begin();
    return end - begin;
  }
};

// Accepted
// 751/751 cases passed (206 ms)
// Your runtime beats 83.45 % of cpp submissions
// Your memory usage beats 98.31 % of cpp submissions (414.6 MB)
Algorithm