C++ Program to Remove All Occurrences of an Element in an Array

Given an array and a target element, the task is to remove all occurrences of the target element while preserving the order of the remaining elements.

All elements equal to the target are removed.
The function can either create a new array or modify the original array in place.

Examples

Input: {1, 4, 3, 6, 8, 3, 9, 10, 3, 3, 7}
target=3
Output: {1, 4, 6, 8, 9, 10, 7}
Input: {12, 11, 10, 17, 12, 4, 7, 12}
target=12
Output: {11, 10, 17, 4, 7}

Approaches to Remove All Occurrences

The problem can be solved using an auxiliary array or by shifting the remaining elements within the original array.

Removing Elements Using an Auxiliary Array

In this approach, create a temporary array and copy only the elements that are different from the target.

Steps:

Traverse the array and count the elements equal to the target.
Create a temporary array with enough space for the remaining elements.
Traverse the original array again and copy only the non-target elements.
Print the resulting array.

C++

#include <iostream>
using namespace std;

void removeAllOccurrences(int arr[], int target, int n)
{
    int count = 0;

    // Count occurrences of target
    for (int i = 0; i < n; i++)
    {
        if (arr[i] == target)
            count++;
    }

    int newSize = n - count;
    int temp[newSize];
    int index = 0;

    // Copy non-target elements
    for (int i = 0; i < n; i++)
    {
        if (arr[i] != target)
            temp[index++] = arr[i];
    }

    // Print the resulting array
    for (int i = 0; i < newSize; i++)
        cout << temp[i] << " ";
}

int main()
{
    int arr[] = {1, 4, 3, 6, 8, 3, 9, 10, 3, 3, 7};
    int target = 3;

    int n = sizeof(arr) / sizeof(arr[0]);

    removeAllOccurrences(arr, target, n);

    return 0;
}

Output

1 4 6 8 9 10 7

1 4 6 8 9 10 7

Explanation: The first traversal counts how many times the target occurs, which determines the size of the resulting array. The second traversal copies only the elements that are not equal to the target into temp[]. The original array remains unchanged.

Removing Elements Using In-Place Shifting

The array can also be modified without using an additional array. A separate counter keeps track of how many target elements have been encountered.