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Kotlin-based LeetCode algorithm problem solutions, regularly updated
2671\. Frequency Tracker
Medium
Design a data structure that keeps track of the values in it and answers some queries regarding their frequencies.
Implement the `FrequencyTracker` class.
* `FrequencyTracker()`: Initializes the `FrequencyTracker` object with an empty array initially.
* `void add(int number)`: Adds `number` to the data structure.
* `void deleteOne(int number)`: Deletes **one** occurrence of `number` from the data structure. The data structure **may not contain** `number`, and in this case nothing is deleted.
* `bool hasFrequency(int frequency)`: Returns `true` if there is a number in the data structure that occurs `frequency` number of times, otherwise, it returns `false`.
**Example 1:**
**Input** ["FrequencyTracker", "add", "add", "hasFrequency"] [[], [3], [3], [2]]
**Output:** [null, null, null, true]
**Explanation:**
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.add(3); // The data structure now contains [3]
frequencyTracker.add(3); // The data structure now contains [3, 3]
frequencyTracker.hasFrequency(2); // Returns true, because 3 occurs twice
**Example 2:**
**Input** ["FrequencyTracker", "add", "deleteOne", "hasFrequency"] [[], [1], [1], [1]]
**Output:** [null, null, null, false]
**Explanation:**
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.add(1); // The data structure now contains [1]
frequencyTracker.deleteOne(1); // The data structure becomes empty []
frequencyTracker.hasFrequency(1); // Returns false, because the data structure is empty
**Example 3:**
**Input** ["FrequencyTracker", "hasFrequency", "add", "hasFrequency"] [[], [2], [3], [1]]
**Output:** [null, false, null, true]
**Explanation:**
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.hasFrequency(2); // Returns false, because the data structure is empty
frequencyTracker.add(3); // The data structure now contains [3]
frequencyTracker.hasFrequency(1); // Returns true, because 3 occurs once
**Constraints:**
* 1 <= number <= 105
* 1 <= frequency <= 105
* At most, 2 * 105 calls will be made to `add`, `deleteOne`, and `hasFrequency` in **total**.