Merge Sort Hack

• Binary Search Hack 1
• Merge Sort Hack 2 (my own hack)

Binary Search Hack 1

void merge(MyObject arr[], int l, int m, int r)
{
    // Find the sizes of two subarrays to be merged
    int n1 = m - l + 1;
    int n2 = r - m;

    /* Create temp arrays */
    MyObject[] L = new MyObject[n1];
    MyObject[] R = new MyObject[n2];

    /* Copy data to temp arrays */
    for (int i = 0; i < n1; ++i)
        L[i] = arr[l + i];
    for (int j = 0; j < n2; ++j)
        R[j] = arr[m + 1 + j];

    /* Merge the temp arrays */

    // Initial indexes of first and second subarrays
    int i = 0, j = 0;

    // Initial index of merged subarray array
    int k = l;
    while (i < n1 && j < n2) {
        if (L[i].compareTo(R[j]) <= 0) {
            arr[k] = L[i];
            i++;
        }
        else {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    /* Copy remaining elements of L[] if any */
    while (i < n1) {
        arr[k] = L[i];
        i++;
        k++;
    }

    /* Copy remaining elements of R[] if any */
    while (j < n2) {
        arr[k] = R[j];
        j++;
        k++;
    }
}

Merge Sort Hack 2 (my own hack)

Creating my own hack: Create an optimization that can be made to the standard merge sort algorithm to use a different sorting algorithm for small sub-arrays, rather than recursively applying merge sort to all sub-arrays. This can improve performance by reducing the overhead of function calls and memory allocation.

import java.util.Arrays;

public class MergeSortHack {

    public static int[] mergeSortHack(int[] arr) {
        if (arr.length <= 1) {
            return arr;
        }

        if (arr.length < 20) { // Sort small sub-arrays with insertion sort
            for (int i = 1; i < arr.length; i++) {
                int key = arr[i];
                int j = i - 1;
                while (j >= 0 && arr[j] > key) {
                    arr[j + 1] = arr[j];
                    j--;
                }
                arr[j + 1] = key;
            }
            return arr;
        }

        int mid = arr.length / 2;
        int[] left = Arrays.copyOfRange(arr, 0, mid);
        int[] right = Arrays.copyOfRange(arr, mid, arr.length);
        left = mergeSortHack(left);
        right = mergeSortHack(right);
        return merge(left, right);
    }

    public static int[] merge(int[] left, int[] right) {
        int[] result = new int[left.length + right.length];
        int i = 0, j = 0, k = 0;
        while (i < left.length && j < right.length) {
            if (left[i] <= right[j]) {
                result[k] = left[i];
                i++;
            } else {
                result[k] = right[j];
                j++;
            }
            k++;
        }
        while (i < left.length) {
            result[k] = left[i];
            i++;
            k++;
        }
        while (j < right.length) {
            result[k] = right[j];
            j++;
            k++;
        }
        return result;
    }

    public static void main(String[] args) {
        int[] arr = {9, 2, 5, 1, 3, 8, 6, 4, 7};
        System.out.println("Before sorting: " + Arrays.toString(arr));
        int[] sortedArr = mergeSortHack(arr);
        System.out.println("After sorting: " + Arrays.toString(sortedArr));
    }
}