|
| 1 | +/** |
| 2 | + * In an exam room, there are N seats in a single row, numbered 0, 1, 2, ..., N-1. |
| 3 | + * |
| 4 | + * When a student enters the room, they must sit in the seat that maximizes the |
| 5 | + * distance to the closest person. If there are multiple such seats, they sit |
| 6 | + * in the seat with the lowest number. (Also, if no one is in the room, then |
| 7 | + * the student sits at seat number 0.) |
| 8 | + * |
| 9 | + * Return a class ExamRoom(int N) that exposes two functions: ExamRoom.seat() |
| 10 | + * returning an int representing what seat the student sat in, and |
| 11 | + * ExamRoom.leave(int p) representing that the student in seat number p now |
| 12 | + * leaves the room. It is guaranteed that any calls to ExamRoom.leave(p) have |
| 13 | + * a student sitting in seat p. |
| 14 | + * |
| 15 | + * Example 1: |
| 16 | + * Input: ["ExamRoom","seat","seat","seat","seat","leave","seat"], [[10],[],[],[],[],[4],[]] |
| 17 | + * Output: [null,0,9,4,2,null,5] |
| 18 | + * |
| 19 | + * Explanation: |
| 20 | + * ExamRoom(10) -> null |
| 21 | + * seat() -> 0, no one is in the room, then the student sits at seat number 0. |
| 22 | + * seat() -> 9, the student sits at the last seat number 9. |
| 23 | + * seat() -> 4, the student sits at the last seat number 4. |
| 24 | + * seat() -> 2, the student sits at the last seat number 2. |
| 25 | + * leave(4) -> null |
| 26 | + * seat() -> 5, the student sits at the last seat number 5. |
| 27 | + * |
| 28 | + * Note: |
| 29 | + * 1 <= N <= 10^9 |
| 30 | + * ExamRoom.seat() and ExamRoom.leave() will be called at most 10^4 times across all test cases. |
| 31 | + * Calls to ExamRoom.leave(p) are guaranteed to have a student currently sitting in seat number p. |
| 32 | + */ |
| 33 | + |
| 34 | + |
| 35 | +public class ExamRoom855 { |
| 36 | + class ExamRoom { |
| 37 | + private PriorityQueue<Range> pq; |
| 38 | + private Map<Integer, Range> lefts; |
| 39 | + private Map<Integer, Range> rights; |
| 40 | + private int N; |
| 41 | + |
| 42 | + public ExamRoom(int N) { |
| 43 | + this.pq = new PriorityQueue(1, new Comparator<Range>() { |
| 44 | + @Override |
| 45 | + public int compare(Range r1, Range r2) { |
| 46 | + int rangeDiff = Integer.compare(dis(r2), dis(r1)); |
| 47 | + if (rangeDiff != 0) return rangeDiff; |
| 48 | + return Integer.compare(r1.left, r2.left); |
| 49 | + } |
| 50 | + }); |
| 51 | + this.lefts = new HashMap<>(); |
| 52 | + this.rights = new HashMap<>(); |
| 53 | + this.N = N; |
| 54 | + |
| 55 | + Range first = new Range(-1, N); |
| 56 | + this.pq.add(first); |
| 57 | + this.lefts.put(first.left, first); |
| 58 | + this.rights.put(first.right, first); |
| 59 | + } |
| 60 | + |
| 61 | + public int seat() { |
| 62 | + if (this.pq.isEmpty()) return -1; |
| 63 | + Range curr = this.pq.poll(); |
| 64 | + this.lefts.remove(curr.left); |
| 65 | + this.rights.remove(curr.right); |
| 66 | + |
| 67 | + int pos = sitPos(curr); |
| 68 | + Range l = new Range(curr.left, pos); |
| 69 | + this.lefts.put(l.left, l); |
| 70 | + this.rights.put(l.right, l); |
| 71 | + if (curr.left + 1 < pos) { |
| 72 | + this.pq.add(l); |
| 73 | + } |
| 74 | + |
| 75 | + Range r = new Range(pos, curr.right); |
| 76 | + this.lefts.put(r.left, r); |
| 77 | + this.rights.put(r.right, r); |
| 78 | + if (pos + 1 < curr.right) { |
| 79 | + this.pq.add(r); |
| 80 | + } |
| 81 | + return pos; |
| 82 | + } |
| 83 | + |
| 84 | + public void leave(int p) { |
| 85 | + Range r = this.lefts.get(p); |
| 86 | + Range l = this.rights.get(p); |
| 87 | + this.pq.remove(r); |
| 88 | + this.pq.remove(l); |
| 89 | + |
| 90 | + Range merged = new Range(l.left, r.right); |
| 91 | + this.pq.add(merged); |
| 92 | + this.lefts.put(merged.left, merged); |
| 93 | + this.rights.put(merged.right, merged); |
| 94 | + } |
| 95 | + |
| 96 | + private int sitPos(Range r) { |
| 97 | + return sitPos(r.left, r.right); |
| 98 | + } |
| 99 | + |
| 100 | + private int sitPos(int left, int right) { |
| 101 | + if (left + 1 >= right) return -1; |
| 102 | + if (left < 0) return 0; |
| 103 | + if (right >= this.N) return this.N - 1; |
| 104 | + return (right - left) / 2 + left; |
| 105 | + } |
| 106 | + |
| 107 | + private int dis(Range r) { |
| 108 | + return dis(r.left, r.right); |
| 109 | + } |
| 110 | + |
| 111 | + private int dis(int left, int right) { |
| 112 | + if (left < 0) return right; |
| 113 | + if (right >= this.N) return this.N - 1 - left; |
| 114 | + return (right - left) / 2; |
| 115 | + } |
| 116 | + } |
| 117 | + |
| 118 | + class Range { |
| 119 | + int left; |
| 120 | + int right; |
| 121 | + Range (int l, int r) { |
| 122 | + this.left = l; |
| 123 | + this.right = r; |
| 124 | + } |
| 125 | + } |
| 126 | + |
| 127 | +/** |
| 128 | + * Your ExamRoom object will be instantiated and called as such: |
| 129 | + * ExamRoom obj = new ExamRoom(N); |
| 130 | + * int param_1 = obj.seat(); |
| 131 | + * obj.leave(p); |
| 132 | + */ |
| 133 | + |
| 134 | +} |
0 commit comments