Package g2601_2700.s2671_frequency_tracker

Class FrequencyTracker

  • public class FrequencyTracker
extends Object
    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.

    • Constructor Detail

      • FrequencyTracker

        public FrequencyTracker()

    • Method Detail

      • add

        public void add​(int number)

      • deleteOne

        public void deleteOne​(int number)

      • hasFrequency

        public boolean hasFrequency​(int frequency)