g2601_2700.s2671_frequency_tracker.FrequencyTracker Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of leetcode-in-java21 Show documentation
Java-based LeetCode algorithm problem solutions, regularly updated
There is a newer version: 1.38
package g2601_2700.s2671_frequency_tracker;

// #Medium #Hash_Table #Design #2023_09_10_Time_31_ms_(83.08%)_Space_111.8_MB_(59.70%)

import java.util.HashMap;
import java.util.Map;

/**
 * 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**.
**/
public class FrequencyTracker {
    private final Map numCount;
    private final Map frequencies;

    public FrequencyTracker() {
        numCount = new HashMap<>();
        frequencies = new HashMap<>();
    }

    public void add(int number) {
        int newCount = numCount.merge(number, 1, Integer::sum);
        frequencies.merge(newCount, 1, Integer::sum);
        if (newCount > 1) {
            frequencies.merge(newCount - 1, -1, Integer::sum);
        }
    }

    public void deleteOne(int number) {
        Integer currentVal = numCount.get(number);
        if (currentVal != null && currentVal > 0) {
            int newCount = numCount.merge(number, -1, Integer::sum);
            frequencies.merge(newCount, 1, Integer::sum);
            frequencies.merge(newCount + 1, -1, Integer::sum);
        }
    }

    public boolean hasFrequency(int frequency) {
        Integer existing = frequencies.get(frequency);
        return existing != null && existing > 0;
    }
}

/*
 * Your FrequencyTracker object will be instantiated and called as such:
 * FrequencyTracker obj = new FrequencyTracker();
 * obj.add(number);
 * obj.deleteOne(number);
 * boolean param_3 = obj.hasFrequency(frequency);
 */