Remove duplicated from sorted array

Author: kshitizsaini113

src/main/java/array/remove_duplicates_from_sorted_array/RemoveDuplicates.java

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+package array.remove_duplicates_from_sorted_array;
+
+/**
+ * Provides a method to remove duplicate elements from a sorted integer array
+ * in-place such that each unique element appears only once.
+ *
+ * <p>The method preserves the relative order of elements and returns the
+ * number of unique elements. The first {@code k} positions of the array
+ * will contain the unique elements in sorted order.</p>
+ *
+ * <p>Constraints:
+ * <ul>
+ *   <li>The input array must be sorted in non-decreasing order.</li>
+ *   <li>The operation is performed in-place with O(1) extra space.</li>
+ * </ul>
+ * </p>
+ */
+public class RemoveDuplicates {
+
+    /**
+     * Removes duplicates from a sorted integer array in-place.
+     *
+     * <p>After execution:
+     * <ul>
+     *   <li>The first {@code k} elements of {@code nums} contain unique values.</li>
+     *   <li>The remaining elements beyond index {@code k - 1} are unspecified.</li>
+     * </ul>
+     * </p>
+     *
+     * @param nums a sorted array of integers in non-decreasing order
+     * @return the number of unique elements in the array
+     * @throws NullPointerException if {@code nums} is {@code null}
+     */
+    public int removeDuplicates(int[] nums) {
+        if (nums.length == 0 || nums.length == 1) {
+            return nums.length;
+        }
+
+        int idx = 0;
+        for (int i = 1; i < nums.length; i++) {
+            if (nums[i] != nums[idx]) {
+                idx++;
+                nums[idx] = nums[i];
+            }
+        }
+        return ++idx;
+    }
+}

src/main/java/array/remove_duplicates_from_sorted_array/package-info.java

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+/**
+ * Contains algorithms related to array manipulation.
+ *
+ * <p>This package focuses on in-place array operations that optimize
+ * space complexity. The primary problem addressed here is removing
+ * duplicate elements from a sorted array while maintaining order.</p>
+ *
+ * <p>Example use cases include:
+ * <ul>
+ *   <li>Data normalization</li>
+ *   <li>Preprocessing sorted datasets</li>
+ *   <li>Optimizing memory usage</li>
+ * </ul>
+ * </p>
+ */
+package array.remove_duplicates_from_sorted_array;

src/test/java/array/remove_duplicates_from_sorted_array/RemoveDuplicatesTest.java

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+package array.remove_duplicates_from_sorted_array;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Unit tests for {@link RemoveDuplicates}.
+ */
+class RemoveDuplicatesTest {
+
+    private final RemoveDuplicates solution = new RemoveDuplicates();
+
+    @Test
+    void testArrayWithDuplicates() {
+        int[] nums = {1, 1, 2, 2, 3};
+        int k = solution.removeDuplicates(nums);
+
+        assertEquals(3, k);
+        assertArrayEquals(new int[]{1, 2, 3}, copyFirstK(nums, k));
+    }
+
+    @Test
+    void testArrayWithoutDuplicates() {
+        int[] nums = {1, 2, 3, 4};
+        int k = solution.removeDuplicates(nums);
+
+        assertEquals(4, k);
+        assertArrayEquals(new int[]{1, 2, 3, 4}, copyFirstK(nums, k));
+    }
+
+    @Test
+    void testSingleElementArray() {
+        int[] nums = {5};
+        int k = solution.removeDuplicates(nums);
+
+        assertEquals(1, k);
+        assertArrayEquals(new int[]{5}, copyFirstK(nums, k));
+    }
+
+    @Test
+    void testEmptyArray() {
+        int[] nums = {};
+        int k = solution.removeDuplicates(nums);
+
+        assertEquals(0, k);
+    }
+
+    @Test
+    void testAllElementsSame() {
+        int[] nums = {2, 2, 2, 2};
+        int k = solution.removeDuplicates(nums);
+
+        assertEquals(1, k);
+        assertArrayEquals(new int[]{2}, copyFirstK(nums, k));
+    }
+
+    /**
+     * Utility method to copy the first k elements from an array.
+     */
+    private int[] copyFirstK(int[] nums, int k) {
+        int[] result = new int[k];
+        System.arraycopy(nums, 0, result, 0, k);
+        return result;
+    }
+}