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1801. Number of Orders in the Backlog

  • Time: $O(n\log n)$
  • Space: $O(n)$
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class Solution {
 public:
  int getNumberOfBacklogOrders(vector<vector<int>>& orders) {
    constexpr int kMod = 1'000'000'007;
    int ans = 0;
    priority_queue<vector<int>> buysMaxHeap;
    priority_queue<vector<int>, vector<vector<int>>, greater<>> sellsMinHeap;

    for (const vector<int>& order : orders) {
      if (order[2] == 0)
        buysMaxHeap.push(order);
      else
        sellsMinHeap.push(order);
      while (!buysMaxHeap.empty() && !sellsMinHeap.empty() &&
             buysMaxHeap.top()[0] >= sellsMinHeap.top()[0]) {
        const int minAmount = min(buysMaxHeap.top()[1], sellsMinHeap.top()[1]);
        vector<int> buysMaxHeapTop = buysMaxHeap.top();
        buysMaxHeap.pop();
        buysMaxHeapTop[1] -= minAmount;
        if (buysMaxHeapTop[1] > 0)
          buysMaxHeap.push(buysMaxHeapTop);

        vector<int> sellsMinHeapTop = sellsMinHeap.top();
        sellsMinHeap.pop();
        sellsMinHeapTop[1] -= minAmount;
        if (sellsMinHeapTop[1] > 0)
          sellsMinHeap.push(sellsMinHeapTop);
      }
    }

    while (!buysMaxHeap.empty()) {
      ans += buysMaxHeap.top()[1], buysMaxHeap.pop();
      ans %= kMod;
    }

    while (!sellsMinHeap.empty()) {
      ans += sellsMinHeap.top()[1], sellsMinHeap.pop();
      ans %= kMod;
    }

    return ans;
  }
};

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class Solution {
  public int getNumberOfBacklogOrders(int[][] orders) {
    final int kMod = 1_000_000_007;
    int ans = 0;
    Queue<int[]> buysMaxHeap = new PriorityQueue<>((a, b) -> Integer.compare(b[0], a[0]));
    Queue<int[]> sellsMinHeap = new PriorityQueue<>((a, b) -> Integer.compare(a[0], b[0]));

    for (int[] order : orders) {
      if (order[2] == 0)
        buysMaxHeap.offer(order);
      else
        sellsMinHeap.offer(order);
      while (!buysMaxHeap.isEmpty() && !sellsMinHeap.isEmpty() &&
             buysMaxHeap.peek()[0] >= sellsMinHeap.peek()[0]) {
        final int minAmount = Math.min(buysMaxHeap.peek()[1], sellsMinHeap.peek()[1]);
        buysMaxHeap.peek()[1] -= minAmount;
        sellsMinHeap.peek()[1] -= minAmount;
        if (buysMaxHeap.peek()[1] == 0)
          buysMaxHeap.poll();
        if (sellsMinHeap.peek()[1] == 0)
          sellsMinHeap.poll();
      }
    }

    while (!buysMaxHeap.isEmpty()) {
      ans += buysMaxHeap.poll()[1];
      ans %= kMod;
    }

    while (!sellsMinHeap.isEmpty()) {
      ans += sellsMinHeap.poll()[1];
      ans %= kMod;
    }

    return ans;
  }
}