Merge Sort Hack #1

void merge(String 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 */
    String[] L = new String[n1];
    String[] R = new String[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

public class MergeSort {

    public static void mergeSort(int[] arr, int left, int right) {
        if (left < right) {
            int mid = (left + right) / 2;
            mergeSort(arr, left, mid);
            mergeSort(arr, mid + 1, right);
            merge(arr, left, mid, right);
        }
    }

    public static void merge(int[] arr, int left, int mid, int right) {
        int n1 = mid - left + 1;
        int n2 = right - mid;

        int[] leftArr = new int[n1];
        int[] rightArr = new int[n2];

        for (int i = 0; i < n1; i++) {
            leftArr[i] = arr[left + i];
        }
        for (int j = 0; j < n2; j++) {
            rightArr[j] = arr[mid + 1 + j];
        }

        int i = 0, j = 0, k = left;
        while (i < n1 && j < n2) {
            if (leftArr[i] <= rightArr[j]) {
                arr[k] = leftArr[i];
                i++;
            } else {
                arr[k] = rightArr[j];
                j++;
            }
            k++;
        }

        while (i < n1) {
            arr[k] = leftArr[i];
            i++;
            k++;
        }

        while (j < n2) {
            arr[k] = rightArr[j];
            j++;
            k++;
        }
    }

    public static void main(String[] args) {
        int[] arr = {10, 7, 8, 9, 1, 5};
        System.out.println("Before:" + Arrays.toString(arr));
        mergeSort(arr, 0, arr.length - 1);
        System.out.println("After:" + Arrays.toString(arr));
    }
}
MergeSort.main(null);

Before:[10, 7, 8, 9, 1, 5]
After:[1, 5, 7, 8, 9, 10]

Binary Search Hack #1

public class BinarySearchRecursive {
    public static int binarySearch(int[] arr, int x, int low, int high) {
        if (low > high) {
            return -1; // Element not found
        }
        
        int mid = low + (high - low) / 2;
        if (arr[mid] == x) {
            return mid; // Element found at mid index
        } else if (arr[mid] > x) {
            return binarySearch(arr, x, low, mid - 1); // Search in left half
        } else {
            return binarySearch(arr, x, mid + 1, high); // Search in right half
        }
    }
    
    public static void main(String[] args) {
        int[] arr = {1, 3, 5, 7, 9, 23, 45, 67};
        int x = 45;
        int index = binarySearch(arr, x, 0, arr.length - 1);
        if (index == -1) {
            System.out.println("Element not found in array");
        } else {
            System.out.println("Element found at index: " + index);
        }
    }
}
BinarySearchRecursive.main(null);

Element found at index: 6

Binary Search Hack #2

public class MergeSortAndBinarySearch {
    public static void main(String[] args) {
        int[] array = {5, 6, 3, 1, 8, 9, 4, 7, 2};
        int searchElement = 7;
        
        // Sort the array using merge sort
        mergeSort(array, 0, array.length - 1);
        
        // Perform binary search on sorted array to find index of searchElement
        int index = binarySearch(array, searchElement, 0, array.length - 1);
        
        if (index == -1) {
            System.out.println("Element not found in array");
        } else {
            System.out.println("Element found at index: " + index);
        }
    }
    
    public static void mergeSort(int[] arr, int left, int right) {
        if (left < right) {
            int mid = left + (right - left) / 2;
            
            mergeSort(arr, left, mid);
            mergeSort(arr, mid + 1, right);
            
            merge(arr, left, mid, right);
        }
    }
    
    public static void merge(int[] arr, int left, int mid, int right) {
        int n1 = mid - left + 1;
        int n2 = right - mid;
        
        int[] leftArr = new int[n1];
        int[] rightArr = new int[n2];
        
        for (int i = 0; i < n1; i++) {
            leftArr[i] = arr[left + i];
        }
        for (int j = 0; j < n2; j++) {
            rightArr[j] = arr[mid + 1 + j];
        }
        
        int i = 0, j = 0, k = left;
        while (i < n1 && j < n2) {
            if (leftArr[i] <= rightArr[j]) {
                arr[k++] = leftArr[i++];
            } else {
                arr[k++] = rightArr[j++];
            }
        }
        
        while (i < n1) {
            arr[k++] = leftArr[i++];
        }
        
        while (j < n2) {
            arr[k++] = rightArr[j++];
        }
    }
    
    public static int binarySearch(int[] arr, int x, int low, int high) {
        if (low > high) {
            return -1; // Element not found
        }
        
        int mid = low + (high - low) / 2;
        if (arr[mid] == x) {
            return mid; // Element found at mid index
        } else if (arr[mid] > x) {
            return binarySearch(arr, x, low, mid - 1); // Search in left half
        } else {
            return binarySearch(arr, x, mid + 1, high); // Search in right half
        }
    }
}
MergeSortAndBinarySearch.main(null);

Element found at index: 6