Exam Room LeetCode solution in C++

1
class ExamRoom {
2
 public:
3
  set<int> s; // ordered set
4
  int num;
5
  ExamRoom(int n) {
6
    num = n; // total seats
7
  }
8

9
  int seat() {
10
    if (s.size() == 0) {
11
      s.insert(0);
12
      return 0;
13
    } // if size is zero place at seat 0
14
    auto itr = s.begin();
15
    if (s.size() == 1) { // if size==1 -> check if its closer to 0 or last seat (num-1)
16
      if (*itr > num - 1 - (*itr)) {
17
        s.insert(0);
18
        return 0;
19
      } else {
20
        s.insert(num - 1);
21
        return num - 1;
22
      }
23
    }
24
    int mx = -1; // for max gap
25
    int l = 0;   // for left index of the student to max gap.
26

27
    if (s.find(0) == s.end()) {
28
      mx = (*itr);
29
      l = -mx;
30
    } // if 0 is not seated -> check gap with 0 and starting seat.
31

32
    // Iterate the set to calculate gaps
33
    for (int i = 0; i < s.size() - 1; i++) {
34
      int a = *itr; // seat number  for 1st element
35
      itr++;
36
      int b = *itr; // seat number of next element in the set
37

38
      // check the gap and update
39
      if (mx < (b - a) / 2) {
40
        mx = (b - a) / 2;
41
        l = a;
42
      }
43
    }
44
    if (s.find(num - 1) == s.end()) { // if last seat is vacant -> check gap
45
                                      // with last filled seat and (num-1)
46
      if (mx < num - 1 - (*itr)) {
47
        mx = (num - 1 - (*itr));
48
        l = *itr;
49
      }
50
    }
51
    s.insert(l + mx); // place the student at l+mx
52
    return l + mx;
53
  }
54

55
  void leave(int p) {
56
    // remove student from set
57
    s.erase(p);
58
  }
59
};