Add a Solution for Remove Element (LeetCode Problem 27)

dsa-solutions/lc-solutions/0000-0099/0027-Remove-Element.md

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+---
+id: remove-element
+title: Remove Element (LeetCode)
+sidebar_label: 0027-RemoveElement
+difficulty: Easy
+---
+
+## Problem Description
+
+
+| Problem Statement | Solution Link | LeetCode Profile |
+| :---------------- | :------------ | :--------------- |
+| [Merge Two Sorted Lists](https://leetcode.com/problems/remove-element/) | [Merge Two Sorted Lists Solution on LeetCode](https://leetcode.com/problems/remove-element/solutions/) |  [VijayShankerSharma](https://leetcode.com/u/darkknight648/) |
+
+## Problem Description
+
+Given an integer array `nums` and an integer `val`, remove all occurrences of `val` in `nums` in-place. The order of the elements may be changed. Then return the number of elements in `nums` which are not equal to `val`.
+
+Consider the number of elements in `nums` which are not equal to `val` 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 elements which are not equal to `val`. 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 val = ...; // Value to remove
+int[] expectedNums = [...]; // The expected answer with correct length.
+                            // It is sorted with no values equaling val.
+
+int k = removeElement(nums, val); // Calls your implementation
+
+assert k == expectedNums.length;
+sort(nums, 0, k); // Sort the first k elements of nums
+for (int i = 0; i < actualLength; i++) {
+    assert nums[i] == expectedNums[i];
+}
+```
+
+If all assertions pass, then your solution will be accepted.
+
+### Examples
+
+#### Example 1
+
+- **Input:** `nums = [3,2,2,3], val = 3`
+- **Output:** `2, nums = [2,2,_,_]`
+- **Explanation:** Your function should return `k = 2`, with the first two elements of `nums` being 2. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+#### Example 2
+
+- **Input:** `nums = [0,1,2,2,3,0,4,2], val = 2`
+- **Output:** `5, nums = [0,1,4,0,3,_,_,_]`
+- **Explanation:** Your function should return `k = 5`, with the first five elements of `nums` containing 0, 0, 1, 3, and 4. Note that the five elements can be returned in any order. It does not matter what you leave beyond the returned `k` (hence they are underscores).
+
+### Constraints
+
+- `0 <= nums.length <= 100`
+- `0 <= nums[i] <= 50`
+- `0 <= val <= 100`
+
+### Approach
+
+To solve the problem, we can use the following approach:
+
+1. **Initialize Two Pointers:**
+   - Use two pointers, `slow` and `fast`, where `slow` points to the beginning of the array and `fast` moves forward to explore the array.
+
+2. **Iterate Through the Array:**
+   - While `fast` is within the bounds of the array:
+     - If `nums[fast]` is not equal to `val`, copy `nums[fast]` to `nums[slow]` and increment both pointers.
+     - If `nums[fast]` is equal to `val`, just increment `fast`.
+
+3. **Return Result:**
+   - The new length of the array without the elements equal to `val` is given by `slow`.
+
+### Solution Code
+
+#### Python
+
+```
+class Solution(object):
+    def removeElement(self, nums, val):
+        slow = 0
+
+        for fast in range(len(nums)):
+            if nums[fast] != val:
+                nums[slow] = nums[fast]
+                slow += 1
+
+        return slow
+```
+
+#### Java
+
+```
+class Solution {
+    public int removeElement(int[] nums, int val) {
+        int slow = 0;
+
+        for (int fast = 0; fast < nums.length; fast++) {
+            if (nums[fast] != val) {
+                nums[slow] = nums[fast];
+                slow++;
+            }
+        }
+
+        return slow;
+    }
+}
+```
+
+#### C++
+
+```
+class Solution {
+public:
+    int removeElement(vector<int>& nums, int val) {
+        int slow = 0;
+
+        for (int fast = 0; fast < nums.size(); fast++) {
+            if (nums[fast] != val) {
+                nums[slow] = nums[fast];
+                slow++;
+            }
+        }
+
+        return slow;
+    }
+};
+```
+
+### Conclusion
+
+The above solution efficiently removes all occurrences of a specified value from an integer 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 an element from an array.