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| 1 | +class MyCalendar { |
| 2 | + |
| 3 | + class Node { |
| 4 | + int start; |
| 5 | + int end; |
| 6 | + Node left,right; |
| 7 | + |
| 8 | + public Node(int start,int end){ |
| 9 | + this.start = start; |
| 10 | + this.end = end; |
| 11 | + } |
| 12 | + } |
| 13 | + |
| 14 | + Node root; |
| 15 | + |
| 16 | + public MyCalendar() { |
| 17 | + |
| 18 | + } |
| 19 | + |
| 20 | + public boolean book(int start, int end) { |
| 21 | + if(root == null){ |
| 22 | + root = new Node(start,end); |
| 23 | + return true; |
| 24 | + } |
| 25 | + Node curr = root; |
| 26 | + while(curr != null){ |
| 27 | + if(end <= curr.start){ |
| 28 | + if(curr.left == null){ |
| 29 | + curr.left = new Node(start,end); |
| 30 | + return true; |
| 31 | + } |
| 32 | + curr = curr.left; |
| 33 | + } |
| 34 | + else if(start >= curr.end){ |
| 35 | + if(curr.right == null){ |
| 36 | + curr.right = new Node(start,end); |
| 37 | + return true; |
| 38 | + } |
| 39 | + curr = curr.right; |
| 40 | + } |
| 41 | + else return false; |
| 42 | + } |
| 43 | + return false; |
| 44 | + } |
| 45 | +} |
| 46 | + |
| 47 | + |
| 48 | + |
| 49 | +/** |
| 50 | +
|
| 51 | +This implementation of `MyCalendar` uses a binary search tree (BST) to efficiently manage the booking of events without overlapping. Each node in the tree represents an event, with `start` and `end` representing the start and end times of that event. |
| 52 | +
|
| 53 | +### Explanation: |
| 54 | +
|
| 55 | +#### 1. **Node Class**: |
| 56 | + ```java |
| 57 | + class Node { |
| 58 | + int start; |
| 59 | + int end; |
| 60 | + Node left, right; |
| 61 | +
|
| 62 | + public Node(int start, int end) { |
| 63 | + this.start = start; |
| 64 | + this.end = end; |
| 65 | + } |
| 66 | + } |
| 67 | + ``` |
| 68 | + - Each node stores the `start` and `end` times of an event. |
| 69 | + - `left` points to events that end before this event starts. |
| 70 | + - `right` points to events that start after this event ends. |
| 71 | +
|
| 72 | +#### 2. **Root Initialization**: |
| 73 | + ```java |
| 74 | + Node root; |
| 75 | + ``` |
| 76 | + - The tree has a `root` node, which is initialized as `null` in the constructor. |
| 77 | + |
| 78 | + ```java |
| 79 | + public MyCalendar() {} |
| 80 | + ``` |
| 81 | + - The constructor initializes the `root` of the binary tree as `null` because initially, there are no booked events. |
| 82 | +
|
| 83 | +#### 3. **book Method**: |
| 84 | + The `book` method attempts to add a new event `[start, end)` to the calendar while ensuring there is no overlap with any existing events. |
| 85 | + |
| 86 | + ```java |
| 87 | + public boolean book(int start, int end) { |
| 88 | + if (root == null) { |
| 89 | + root = new Node(start, end); |
| 90 | + return true; |
| 91 | + } |
| 92 | + ``` |
| 93 | + - If the tree is empty (`root == null`), the event is added as the root node, and the method returns `true`. |
| 94 | +
|
| 95 | +#### 4. **Traversing the Tree**: |
| 96 | + The method then traverses the tree to find the correct position for the new event, ensuring no overlap with any existing event. |
| 97 | + |
| 98 | + ```java |
| 99 | + Node curr = root; |
| 100 | + while (curr != null) { |
| 101 | + ``` |
| 102 | + - The method starts at the root and iteratively traverses down the tree. |
| 103 | + |
| 104 | + - **If the new event ends before the current event starts**: |
| 105 | + ```java |
| 106 | + if (end <= curr.start) { |
| 107 | + if (curr.left == null) { |
| 108 | + curr.left = new Node(start, end); |
| 109 | + return true; |
| 110 | + } |
| 111 | + curr = curr.left; |
| 112 | + } |
| 113 | + ``` |
| 114 | + - This means the new event should be placed in the left subtree (since there is no overlap). |
| 115 | + - If the left child is `null`, the new event is inserted as the left child. |
| 116 | + - If not, the traversal continues to the left child. |
| 117 | +
|
| 118 | + - **If the new event starts after the current event ends**: |
| 119 | + ```java |
| 120 | + else if (start >= curr.end) { |
| 121 | + if (curr.right == null) { |
| 122 | + curr.right = new Node(start, end); |
| 123 | + return true; |
| 124 | + } |
| 125 | + curr = curr.right; |
| 126 | + } |
| 127 | + ``` |
| 128 | + - This means the new event should be placed in the right subtree (since there is no overlap). |
| 129 | + - If the right child is `null`, the new event is inserted as the right child. |
| 130 | + - If not, the traversal continues to the right child. |
| 131 | +
|
| 132 | + - **If the new event overlaps with the current event**: |
| 133 | + ```java |
| 134 | + else return false; |
| 135 | + ``` |
| 136 | + - If neither condition holds (i.e., `end > curr.start` and `start < curr.end`), the new event overlaps with an existing one, so the booking fails, and `false` is returned. |
| 137 | +
|
| 138 | +#### 5. **Edge Cases**: |
| 139 | + - If the new event is disjoint from all existing events, it will be inserted in the appropriate position in the BST, either as a left or right child. |
| 140 | + - The tree is traversed using a `while` loop, ensuring that the insertion or conflict detection happens efficiently. |
| 141 | +
|
| 142 | +### Summary: |
| 143 | +- This solution uses a binary search tree (`BST`) to store events, where each node represents an event with a `start` and `end` time. |
| 144 | +- The `book` method tries to insert a new event, ensuring no overlap by checking the relative positions of the new event against existing ones. |
| 145 | +- Time complexity for insertion and search is on average `O(log n)` for balanced trees but can degrade to `O(n)` in the worst case for unbalanced trees. */ |
| 146 | + |
| 147 | + |
| 148 | + |
| 149 | + |
| 150 | + |
| 151 | + |
| 152 | + |
| 153 | + |
| 154 | + |
| 155 | + |
| 156 | + |
| 157 | + |
| 158 | + |
| 159 | + |
| 160 | + |
| 161 | +//option2 |
| 162 | +class MyCalendar { |
| 163 | + TreeMap<Integer, Integer> calendar; |
| 164 | + |
| 165 | + MyCalendar() { |
| 166 | + calendar = new TreeMap(); |
| 167 | + } |
| 168 | + |
| 169 | + public boolean book(int start, int end) { |
| 170 | + Integer prev = calendar.floorKey(start), |
| 171 | + next = calendar.ceilingKey(start); |
| 172 | + if ((prev == null || calendar.get(prev) <= start) && |
| 173 | + (next == null || end <= next)) { |
| 174 | + calendar.put(start, end); |
| 175 | + return true; |
| 176 | + } |
| 177 | + return false; |
| 178 | + } |
| 179 | +} |
| 180 | +/** |
| 181 | +The `MyCalendar` class implements a booking system that allows users to book events, ensuring that no two events overlap. It uses a `TreeMap` to store and manage the events, where the keys represent the start times and the values represent the end times of the booked events. |
| 182 | +
|
| 183 | +Here’s a detailed breakdown of how the class works: |
| 184 | +
|
| 185 | +### 1. **TreeMap Initialization**: |
| 186 | + ```java |
| 187 | + TreeMap<Integer, Integer> calendar; |
| 188 | + ``` |
| 189 | + - `TreeMap` is a data structure that stores key-value pairs and automatically keeps the keys in sorted order. |
| 190 | + - In this case, the keys are event start times, and the values are the corresponding end times. |
| 191 | +
|
| 192 | + ```java |
| 193 | + calendar = new TreeMap(); |
| 194 | + ``` |
| 195 | + - The constructor initializes the `TreeMap` to manage the events. |
| 196 | +
|
| 197 | +### 2. **`book` Method**: |
| 198 | + This method checks if an event can be booked without overlapping any existing events. |
| 199 | +
|
| 200 | + ```java |
| 201 | + public boolean book(int start, int end) |
| 202 | + ``` |
| 203 | + - **Parameters**: |
| 204 | + - `start`: The start time of the new event. |
| 205 | + - `end`: The end time of the new event (exclusive, meaning the event ends right before this time). |
| 206 | +
|
| 207 | + - **Logic**: |
| 208 | + - The method checks if there is any overlap with the previously booked event (`prev`) or the next booked event (`next`). |
| 209 | +
|
| 210 | + ```java |
| 211 | + Integer prev = calendar.floorKey(start), |
| 212 | + next = calendar.ceilingKey(start); |
| 213 | + ``` |
| 214 | + - `prev`: The `floorKey` returns the largest key (start time) that is less than or equal to `start`. This represents the previous event's start time. |
| 215 | + - `next`: The `ceilingKey` returns the smallest key (start time) that is greater than or equal to `start`. This represents the next event's start time. |
| 216 | +
|
| 217 | + Now, the method checks two conditions: |
| 218 | + ```java |
| 219 | + if ((prev == null || calendar.get(prev) <= start) && (next == null || end <= next)) |
| 220 | + ``` |
| 221 | + - **Condition 1**: `(prev == null || calendar.get(prev) <= start)` |
| 222 | + - This checks whether there is no previous event (`prev == null`) or the previous event ends before or at the new event’s start time (`calendar.get(prev) <= start`). |
| 223 | +
|
| 224 | + - **Condition 2**: `(next == null || end <= next)` |
| 225 | + - This checks whether there is no next event (`next == null`) or the new event ends before the next event starts (`end <= next`). |
| 226 | +
|
| 227 | + If both conditions are satisfied (i.e., no overlap with either previous or next events), the event is added to the `calendar`: |
| 228 | + ```java |
| 229 | + calendar.put(start, end); |
| 230 | + return true; |
| 231 | + ``` |
| 232 | +
|
| 233 | + If there is an overlap, the method returns `false`. |
| 234 | +
|
| 235 | +### 3. **Example**: |
| 236 | +```java |
| 237 | +MyCalendar obj = new MyCalendar(); |
| 238 | +boolean result = obj.book(10, 20); // This will return true if the event [10, 20) can be booked. |
| 239 | +``` |
| 240 | +
|
| 241 | +### Summary: |
| 242 | +- The `TreeMap` structure ensures that events are stored in a sorted manner by start time. |
| 243 | +- The `book` method checks if the new event overlaps with the nearest previous and next events using `floorKey` and `ceilingKey`. |
| 244 | +- If there is no overlap, the event is booked (added to the `TreeMap`), and the method returns `true`. If there is an overlap, it returns `false`. |
| 245 | +
|
| 246 | + */ |
| 247 | + |
| 248 | + |
| 249 | + |
| 250 | +/** |
| 251 | + * Your MyCalendar object will be instantiated and called as such: |
| 252 | + * MyCalendar obj = new MyCalendar(); |
| 253 | + * boolean param_1 = obj.book(start,end); |
| 254 | + */ |
| 255 | + |
| 256 | + |
| 257 | + |
| 258 | + |
| 259 | +// option3 -BRUTE FORCE |
| 260 | + class MyCalendar { |
| 261 | + List<int[]> calender; |
| 262 | + public MyCalendar() { |
| 263 | + calender=new ArrayList<>(); |
| 264 | + } |
| 265 | + public boolean book(int start, int end) { |
| 266 | + for(int[] slot:calender){ |
| 267 | + if(end>slot[0] && start<slot[1]){ |
| 268 | + return false; |
| 269 | + } |
| 270 | + } |
| 271 | + calender.add(new int[]{start,end}); |
| 272 | + return true; |
| 273 | + } |
| 274 | +} |
| 275 | + |
| 276 | +/** |
| 277 | + * Your MyCalendar object will be instantiated and called as such: |
| 278 | + * MyCalendar obj = new MyCalendar(); |
| 279 | + * boolean param_1 = obj.book(start,end); |
| 280 | + */ |
| 281 | + |
| 282 | +/** |
| 283 | + * Your MyCalendar object will be instantiated and called as such: |
| 284 | + * MyCalendar obj = new MyCalendar(); |
| 285 | + * boolean param_1 = obj.book(start,end); |
| 286 | + */ |
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