feat: Improvement to mode algorithm #206 (#238)

* fix: Improvement to mode algorithm #206 * Fixed checkstyle errors * Fixed checkstyle errors * Added Code to Read Me file
iluwatar · Jan 11, 2025 · b444a72 · b444a72
1 parent 212b7c4
commit b444a72
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Showing 3 changed files with 60 additions and 51 deletions.
diff --git a/README.md b/README.md
@@ -720,31 +720,32 @@ public class ArrayModeInPlaceSnippet {
 ```java
 public class ArrayModeSnippet {
 
-  /**
-  * Returns the mode of the array.
-  *
-  * @param arr array to find mode in it
-  * @return mode of array
-  */
-  public static int modeArray(int[] arr) {
-    int mode = 0;
-    int maxcount = 0;
-
-    for (int i = 0; i < arr.length; i++) {
-      int count = 0;
+    /**
+     * Private constructor to prevent instantiation.
+     */
+    private ArrayModeSnippet() {
+        throw new IllegalStateException("Utility class");
+    }
 
-      for (int j = 0; j < arr.length; j++) {
-        if (arr[i] == arr[j]) {
-          count++;
+    /**
+     * Returns the mode(s) of the array.
+     * If multiple modes exist, it returns them in a list.
+     */
+    public static List<Integer> modeArray(int[] arr) {
+        int maxCount = 0;
+        HashMap<Integer, Integer> frequencyMap = new HashMap<>();
+        for (int num : arr) {
+            frequencyMap.put(num, frequencyMap.getOrDefault(num, 0) + 1);
+            maxCount = Math.max(maxCount, frequencyMap.get(num));
         }
-      }
-      if (count > maxcount) {
-        maxcount = count;
-        mode = arr[i];
-      }
+        List<Integer> modes = new ArrayList<>();
+        for (Map.Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
+            if (entry.getValue() == maxCount) {
+                modes.add(entry.getKey());
+            }
+        }
+        return modes;
     }
-    return mode;
-  }
 }
 ```
 

diff --git a/src/main/java/array/ArrayModeSnippet.java b/src/main/java/array/ArrayModeSnippet.java
@@ -24,34 +24,40 @@
 
 package array;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
 /**
  * ArrayModeSnippet.
  */
+
 public class ArrayModeSnippet {
 
   /**
-  * Returns the mode of the array.
-  *
-  * @param arr array to find mode in it
-  * @return mode of array
-  */
-  public static int modeArray(int[] arr) {
-    int mode = 0;
-    int maxcount = 0;
-
-    for (int i = 0; i < arr.length; i++) {
-      int count = 0;
+   * Private constructor to prevent instantiation.
+   */
+  private ArrayModeSnippet() {
+    throw new IllegalStateException("Utility class");
+  }
 
-      for (int j = 0; j < arr.length; j++) {
-        if (arr[i] == arr[j]) {
-          count++;
-        }
-      }
-      if (count > maxcount) {
-        maxcount = count;
-        mode = arr[i];
+  /**
+   * Returns the mode(s) of the array.
+   * If multiple modes exist, it returns them in a list.
+   */
+  public static List<Integer> modeArray(int[] arr) {
+    int maxCount = 0;
+    HashMap<Integer, Integer> frequencyMap = new HashMap<>();
+    for (int num : arr) {
+      frequencyMap.put(num, frequencyMap.getOrDefault(num, 0) + 1);
+      maxCount = Math.max(maxCount, frequencyMap.get(num));
+    }
+    List<Integer> modes = new ArrayList<>();
+    for (Map.Entry<Integer, Integer> entry : frequencyMap.entrySet()) {
+      if (entry.getValue() == maxCount) {
+        modes.add(entry.getKey());
       }
     }
-    return mode;
+    return modes;
   }
 }
diff --git a/src/test/java/array/ArrayModeSnippetTest.java b/src/test/java/array/ArrayModeSnippetTest.java
@@ -26,20 +26,22 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import java.util.List;
 import org.junit.jupiter.api.Test;
 
 /**
  * Tests for 30 Seconds of Java code library.
  */
-public class ArrayModeSnippetTest {
+class ArrayModeSnippetTest {
   /**
-  * Test for {@link ArrayModeSnippet #ArrayModeSnippet(int[])}.
-  */
+   * Test for {@link ArrayModeSnippet #ArrayModeSnippet(int[])}.
+   */
   @Test
-    void testModeArray() {
-    assertEquals(2, ArrayModeSnippet.modeArray(new int[]{1, 2, 3, 2, 4, 2, 2}));
-    assertEquals(-8, ArrayModeSnippet.modeArray(new int[]{-43, -8, -8, -10, -8, -65, -9}));
-    assertEquals(0, ArrayModeSnippet.modeArray(new int[]{-4, 0, -2, -1, 0}));
-    assertEquals(1, ArrayModeSnippet.modeArray(new int[]{1, 1, 1, 1, 1, 1}));
+  void testModeArray() {
+    assertEquals(List.of(2), ArrayModeSnippet.modeArray(new int[]{1, 2, 2, 3}));
+    assertEquals(List.of(2, 3), ArrayModeSnippet.modeArray(new int[]{1, 2, 2, 3, 3}));
+    assertEquals(List.of(1, 2, 3, 4), ArrayModeSnippet.modeArray(new int[]{1, 2, 3, 4}));
+    assertEquals(List.of(), ArrayModeSnippet.modeArray(new int[]{}));
+    assertEquals(List.of(-1, -2), ArrayModeSnippet.modeArray(new int[]{-1, -1, -2, -2, -3}));
   }
-}
+}