TheAlgorithms · realDuYuanChao · Aug 20, 2020 · Aug 20, 2020 · Aug 20, 2020
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+package Maths;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+
+/*
+ * Find the mode of an array of numbers
+ * 
+ * The mode of an array of numbers is the most frequently occurring number in the array, 
+ * or the most frequently occurring numbers if there are multiple numbers with the same frequency
+ */
+public class Mode {
+
+	public static void main(String[] args) {
+
+		/* Test array of integers */
+		assert (mode(new int[]{})) == null;
+		assert Arrays.equals(mode(new int[]{5}), new int[]{5});
+		assert Arrays.equals(mode(new int[]{1, 2, 3, 4, 5}), new int[]{1, 2, 3, 4, 5});
+		assert Arrays.equals(mode(new int[]{7, 9, 9, 4, 5, 6, 7, 7, 8}), new int[]{7});
+		assert Arrays.equals(mode(new int[]{7, 9, 9, 4, 5, 6, 7, 7, 9}), new int[]{7, 9});
+
+	}
+
+	/*
+	 * Find the mode of an array of integers
+	 * 
+	 * @param numbers array of integers
+	 * @return mode of the array
+	 */
+	public static int[] mode(int[] numbers) {
+
+		if(numbers.length == 0) return null;
+
+		HashMap<Integer, Integer> count = new HashMap<>();
+
+		for(int num : numbers) {
+			if(count.containsKey(num)) {
+
+				count.put(num, count.get(num) + 1);
+
+			} else {
+
+				count.put(num, 1);
+
+			}
+
+		}
+
+		int max = Collections.max(count.values());
+		ArrayList<Integer> modes = new ArrayList<>();
+
+		for(int num : count.keySet()) {
+			if(count.get(num) == max) {
+				modes.add(num);
+			}
+		}
+		return modes.stream().mapToInt(n -> n).toArray();
+	}
+
+}