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g2601_2700.s2671_frequency_tracker.readme.md Maven / Gradle / Ivy

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**.