How Can I Efficiently Remove Duplicates from an Array Without Using a Set?

Efficiently Removing Duplicates from an Array Without Resorting to Set

You have endeavored to create a customized solution for eliminating duplicate elements from an array, but performance bottlenecks have emerged. To optimize this implementation, we will analyze the shortcomings of your approach and propose alternative strategies.

Analysis of Your Algorithm

Your algorithm attempts to search for duplicates by comparing each element with every subsequent element. This exhaustive comparison results in an O(n^2) time complexity. For large arrays, this strategy can become extremely inefficient.

Optimized Approach

To significantly improve performance, we can consider the following optimization:

1. Utilizing a Hash Map: Implement a hash map to store the unique elements encountered during iteration. As each element is added to the array, check if it already exists as a key in the hash map. If not, add it. This approach enables efficient constant-time lookup operations, reducing the time complexity to O(n).
2. Sorting Before Filtering: Sort the array in ascending order. Now, the duplicate elements will be adjacent to each other. Iterate through the sorted array and eliminate adjacent duplicates, resulting in a linear-time O(n) algorithm.

Alternative Solutions

While the aforementioned optimizations can enhance your algorithm's performance, you may also consider other established techniques:

• Set Collections: As you need to avoid using Set, we won't delve into this option.
• Using a Sorted Collection: Similar to sorting before filtering, leverage a sorted collection like TreeSet or NavigableSet. It automatically maintains a sorted order and allows efficient element retrieval, resulting in O(n log n) complexity.

Implementation

Based on the optimized approach, a modified version of your algorithm utilizing a hash map could be:

public static int[] removeDuplicatesWithoutSet(int[] arr) {

    HashMap<Integer, Boolean> map = new HashMap<>();
    int end = arr.length;

    for (int i = 0; i < end; i++) {
        if (map.containsKey(arr[i])) {
            int shiftLeft = i;
            for (int k = i + 1; k < end; k++, shiftLeft++) {
                arr[shiftLeft] = arr[k];
            }
            end--;
            i--;
        } else {
            map.put(arr[i], true);
        }
    }

    int[] whitelist = new int[end];
    for (int i = 0; i < end; i++) {
        whitelist[i] = arr[i];
    }
    return whitelist;
}

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