Optimize LeetCode 26: Remove Duplicates from Sorted Array

problems/easy/remove_duplicates_from_sorted_array_26/solution.py

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+# Tags: Array, Two Pointers
+from typing import List
+
+
+class Solution:
+    """
+    Remove Duplicates from Sorted Array
+
+    Problem:
+        Given a sorted array nums, remove the duplicates in-place such that each
+        element appears only once. Return the number of unique elements.
+
+    Approach:
+        Since the array is sorted, duplicate elements are always adjacent.
+        We can use two pointers:
+        - read pointer: scans through the array
+        - write pointer: tracks where to place the next unique element
+
+    Complexity:
+        Time: O(n) - single pass through the array
+        Space: O(1) - in-place modification with no extra data structures
+    """
+
+    def remove_duplicates(self, nums: List[int]) -> int:
+        """
+        Removes duplicates from a sorted array in-place.
+
+        Args:
+            nums: A sorted list of integers (may contain duplicates)
+
+        Returns:
+            int: The number of unique elements (k). The first k elements
+                 of nums will contain the unique elements in sorted order.
+
+        Example:
+            Input:  nums = [1,1,2]
+            Output: k = 2, nums = [1,2,_]
+        """
+        # Edge case: empty array
+        if not nums:
+            return 0
+
+        # Initialize write pointer to 1 (second position)
+        # The first element is always unique in a non-empty sorted array
+        write = 1
+
+        # Start read pointer from index 1 (compare with previous element)
+        for read in range(1, len(nums)):
+            # Since array is sorted, duplicates are always adjacent
+            # If current element is different from previous, it's a new unique element
+            if nums[read] != nums[read - 1]:
+                # Copy the unique element to the write position
+                nums[write] = nums[read]
+                # Move write pointer forward for the next unique element
+                write += 1
+
+        # Return the count of unique elements
+        return write

problems/easy/remove_duplicates_from_sorted_array_26/test_solution.py

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+from .solution import Solution
+
+
+class TestSolution:
+    def setup_method(self):
+        self.solution = Solution()
+
+    def test_example_1(self):
+        """Test from LeetCode example 1"""
+        nums = [1, 1, 2]
+        expected_k = 2
+        expected_nums = [1, 2]
+
+        k = self.solution.remove_duplicates(nums)
+
+        assert k == expected_k
+        assert nums[:k] == expected_nums
+
+    def test_example_2(self):
+        """Test from LeetCode example 2"""
+        nums = [0, 0, 1, 1, 1, 2, 2, 3, 3, 4]
+        expected_k = 5
+        expected_nums = [0, 1, 2, 3, 4]
+
+        k = self.solution.remove_duplicates(nums)
+
+        assert k == expected_k
+        assert nums[:k] == expected_nums