Given an integer array arr[] and an integer X the task is to the remove all occurrences of X from arr[] in-place and return the number of elements which are not equal to X. If there are K number of elements which are not equal to X then the input array arr[] should be modified such that the first K elements should contain the elements which are not equal to X and then the remaining elements.

Note: The order of first K elements may be changed.

Examples:

Input: arr[] = {3, 2, 2, 3}, X = 3
Output: 2, arr[] = {2, 2, _, _}
Explanation: The answer is 2 because there are 2 elements which are not equal to 3 and arr[] will be modified such that the first 2 elements contain the elements which are not equal to 3 and remaining elements can contain any element.

Input: arr[] = {0, 1, 3, 0, 2, 2, 4, 2}, X = 2
Output: 5, arr[] = {0, 1, 3, 0, 4, _, _, _}
Explanation: The answer is 5 because there are 5 elements which are not equal to 2 and arr[] will be modified such that the first 5 elements contain the elements which are not equal to 2 and remaining elements can contain any element.

Approach: To solve the problem, follow the below idea:

Step-by-step algorithm:

• Initialize j to 0. This will track the count of the elements not equal to X.
• Iterate over each element in the array using the loop with the index i.
• If nums[i] is not equal to the X set nums[j] = nums[i] and increment j.
• Return j.

Here is the implementation of the above approach:

def removeElement(nums, val):
  
    # Initialize the counter for the 
    # elements not equal to the val    
    k = 0
    for i in range(len(nums)):

        # Place the non-val element 
        # at the kth position
        if nums[i] != val:
            nums[k] = nums[i]  
            
            # Increment the count of 
            # the non-val elements 
            k += 1             
              
    return k 
  
# Sample Input
nums = [0, 1, 3, 0, 2, 2, 4, 2]
val = 2
k = removeElement(nums, val)
print(k)  
print(nums[:k])   

5
[0, 1, 3, 0, 4]

Time Complexity: O(N), where N is the number of elements in arr[]
Auxiliary Space: O(1)