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package com.thealgorithms.maths;

import java.util.ArrayList;

import java.util.Collections;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

/**

* Utility class to calculate the mode(s) of an array of integers.

* <p>

* The mode of an array is the integer value(s) that occur most frequently.

* If multiple values have the same highest frequency, all such values are returned.

* </p>

*/

public final class Mode {

private Mode() {

}

/**

* Computes the mode(s) of the specified array of integers.

* <p>

* If the input array is empty, this method returns {@code null}.

* If multiple numbers share the highest frequency, all are returned in the result array.

* </p>

*

* @param numbers an array of integers to analyze

* @return an array containing the mode(s) of the input array, or {@code null} if the input is empty

*/

public static int[] mode(final int[] numbers) {

if (numbers.length == 0) {

return null;

}

Map<Integer, Integer> count = new HashMap<>();

for (int num : numbers) {

count.put(num, count.getOrDefault(num, 0) + 1);

}

int max = Collections.max(count.values());

List<Integer> modes = new ArrayList<>();

for (final var entry : count.entrySet()) {

if (entry.getValue() == max) {

modes.add(entry.getKey());

}

}

return modes.stream().mapToInt(Integer::intValue).toArray();

}

}