Add a Solution for Removing Duplicates from Sorted Array (LeetCode Problem 26)

dsa-solutions/lc-solutions/0000-0099/0026-Remove-Duplicates-from-Sorted-Array.md

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+---
+id: remove-duplicates-from-sorted-array
+title: Remove Duplicates from Sorted Array (LeetCode)
+sidebar_label: 0026-RemoveDuplicatesFromSortedArray
+tags:
+    - Array
+    - Two Pointers
+description: Given a sorted integer array, remove duplicates in-place and return the new length of the array with unique elements.
+---
+
+## Problem Description
+
+| Problem Statement                                                                                           | Solution Link                                                                                                                               | LeetCode Profile                                   |
+| :----------------------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------ | :------------------------------------------------- |
+| [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)                                         | [Remove Duplicates from Sorted Array Solution on LeetCode](https://leetcode.com/problems/remove-duplicates-from-sorted-array/solutions/) | [VijayShankerSharma](https://leetcode.com/u/darkknight648/) |
+
+### Problem Description
+
+Given an integer array `nums` sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once. The relative order of the elements should be kept the same. Then return the number of unique elements in `nums`.
+
+Consider the number of unique elements of `nums` to be `k`, to get accepted, you need to do the following things:
+- Change the array `nums` such that the first `k` elements of `nums` contain the unique elements in the order they were present in `nums` initially. 
+- The remaining elements of `nums` are not important as well as the size of `nums`.
+- Return `k`.
+
+### Custom Judge
+
+The judge will test your solution with the following code:
+
+```
+int[] nums = [...]; // Input array
+int[] expectedNums = [...]; // The expected answer with correct length
+
+int k = removeDuplicates(nums); // Calls your implementation
+
+assert k == expectedNums.length;
+for (int i = 0; i < k; i++) {
+    assert nums[i] == expectedNums[i];
+}
+```
+
+If all assertions pass, then your solution will be accepted.
+
+### Examples
+
+#### Example 1
+
+- **Input:** `nums = [1,1,2]`
+- **Output:** `2, nums = [1,2,_]`
+- **Explanation:** Your function should return `k = 2`, with the first two elements of `nums` being 1 and 2 respectively. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+#### Example 2
+
+- **Input:** `nums = [0,0,1,1,1,2,2,3,3,4]`
+- **Output:** `5, nums = [0,1,2,3,4,_,_,_,_,_]`
+- **Explanation:** Your function should return `k = 5`, with the first five elements of `nums` being 0, 1, 2, 3, and 4 respectively. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+### Constraints
+
+- `1 <= nums.length <= 3 * 10^4`
+- `-100 <= nums[i] <= 100`
+- `nums` is sorted in non-decreasing order.
+
+### Approach
+
+To solve the problem, we can use the two-pointer technique. Here is the step-by-step approach:
+
+1. **Initialize Pointers:**
+   - Use `uniqueIndex` to track the position to place the next unique element.
+
+2. **Iterate Through the Array:**
+   - Traverse the array starting from the second element.
+   - If the current element is different from the element at `uniqueIndex`, move `uniqueIndex` forward and update it with the current element.
+
+3. **Return Result:**
+   - The number of unique elements is `uniqueIndex + 1`.
+
+### Solution Code
+
+#### Python
+
+```
+class Solution(object):
+    def removeDuplicates(self, nums):
+        if len(nums) == 0:
+            return 0
+
+        unique_index = 0  # Pointer for placing unique elements
+
+        for i in range(1, len(nums)):
+            if nums[i] != nums[unique_index]:
+                # Found a unique element, place it in the next position
+                unique_index += 1
+                nums[unique_index] = nums[i]
+
+        # The number of unique elements is one more than the index of the last unique element
+        return unique_index + 1
+```
+
+#### Java
+```
+class Solution {
+    public int removeDuplicates(int[] nums) {
+        if (nums.length == 0) return 0;
+
+        int uniqueIndex = 0; // Pointer for placing unique elements
+
+        for (int i = 1; i < nums.length; i++) {
+            if (nums[i] != nums[uniqueIndex]) {
+                // Found a unique element, place it in the next position
+                uniqueIndex++;
+                nums[uniqueIndex] = nums[i];
+            }
+        }
+
+        // The number of unique elements is one more than the index of the last unique element
+        return uniqueIndex + 1;
+    }
+}
+```
+
+#### C++
+```
+class Solution {
+public:
+    int removeDuplicates(vector<int>& nums) {
+        if (nums.size() == 0) return 0;
+
+        int uniqueIndex = 0; // Pointer for placing unique elements
+
+        for (int i = 1; i < nums.size(); i++) {
+            if (nums[i] != nums[uniqueIndex]) {
+                // Found a unique element, place it in the next position
+                uniqueIndex++;
+                nums[uniqueIndex] = nums[i];
+            }
+        }
+
+        // The number of unique elements is one more than the index of the last unique element
+        return uniqueIndex + 1;
+    }
+};
+```
+
+### Conclusion
+
+The above solution efficiently removes duplicates from a sorted array in-place. It employs a two-pointer technique to achieve a time complexity of $O(N)$ and a space complexity of $O(1)$. This ensures that the algorithm can handle input sizes up to the upper limit specified in the constraints efficiently, providing a simple yet effective approach to solving the problem of removing duplicates from a sorted array.