Maximum Frequency Stack LeetCode solution in Java

1
class Node {
2
  int data, freq, time;
3

4
  Node(int data, int freq, int time) {
5
    this.data = data;
6
    this.freq = freq;
7
    this.time = time;
8
  }
9
}
10

11
class CompareNode implements Comparator<Node> {
12
  @Override
13
  public int compare(Node a, Node b) {
14
    if (a.freq - b.freq == 0) {
15
      return b.time - a.time;
16
    }
17
    return b.freq - a.freq;
18
  }
19
}
20

21
class FreqStack {
22
  PriorityQueue<Node> pq;
23
  Map<Integer, Node> map;
24
  int c = 0;
25

26
  public FreqStack() {
27
    pq = new PriorityQueue<>(new CompareNode());
28
    map = new HashMap<>();
29
  }
30

31
  public void push(int val) {
32
    c++;
33
    int freq = 1;
34
    if (map.containsKey(val)) {
35
      freq += map.get(val).freq;
36
    }
37
    map.put(val, new Node(val, freq, c));
38
    pq.add(new Node(val, freq, c++));
39
  }
40

41
  public int pop() {
42
    Node r = pq.remove();
43
    Node a = map.get(r.data);
44
    a.freq--;
45
    return r.data;
46
  }
47
}