🚀 Sorting Algorithms: Merge, Heap, and Radix With Code

three different sorting algorithms: Merge Sort, Heap Sort, and Radix Sort. These algorithms are each explained briefly, and the code is provided for each one

Sorting Algorithms

Merge Sort:

Merge Sort is a divide-and-conquer algorithm that divides the input array into two halves, recursively sorts them, and then merges the sorted halves.
Time Complexity: O(n log n)
Space Complexity: O(n)

import java.util.Arrays;

public class MergeSort {
    public static void mergeSort(int[] arr) {
        if (arr.length > 1) {
            int mid = arr.length / 2;
            int[] left = Arrays.copyOfRange(arr, 0, mid);
            int[] right = Arrays.copyOfRange(arr, mid, arr.length);

            mergeSort(left);
            mergeSort(right);

            int i = 0, j = 0, k = 0;
            while (i < left.length && j < right.length) {
                if (left[i] < right[j]) {
                    arr[k++] = left[i++];
                } else {
                    arr[k++] = right[j++];
                }
            }

            while (i < left.length) {
                arr[k++] = left[i++];
            }

            while (j < right.length) {
                arr[k++] = right[j++];
            }
        }
    }

    public static void main(String[] args) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        System.out.println("Original array: " + Arrays.toString(arr));
        mergeSort(arr);
        System.out.println("Sorted array: " + Arrays.toString(arr));
    }
}

Heap Sort:

Heap Sort is based on the binary heap data structure. It builds a max-heap and repeatedly extracts the maximum element from it.
Time Complexity: O(n log n)
Space Complexity: O(1)

import java.util.Arrays;

public class HeapSort {
    public static void heapSort(int[] arr) {
        int n = arr.length;

        // Build a max heap
        for (int i = n / 2 - 1; i >= 0; i--) {
            heapify(arr, n, i);
        }

        // Extract elements from the heap one by one
        for (int i = n - 1; i >= 0; i--) {
            int temp = arr[0];
            arr[0] = arr[i];
            arr[i] = temp;

            heapify(arr, i, 0);
        }
    }

    public static void heapify(int[] arr, int n, int i) {
        int largest = i;
        int left = 2 * i + 1;
        int right = 2 * i + 2;

        if (left < n && arr[left] > arr[largest]) {
            largest = left;
        }

        if (right < n && arr[right] > arr[largest]) {
            largest = right;
        }

        if (largest != i) {
            int swap = arr[i];
            arr[i] = arr[largest];
            arr[largest] = swap;

            heapify(arr, n, largest);
        }
    }

    public static void main(String[] args) {
        int[] arr = {12, 11, 13, 5, 6, 7};
        System.out.println("Original array: " + Arrays.toString(arr));
        heapSort(arr);
        System.out.println("Sorted array: " + Arrays.toString(arr));
    }
}

Radix Sort:

Radix Sort is a non-comparative sorting algorithm that sorts integers by processing individual digits. It can be applied to integers or strings with a fixed length.
Time Complexity: O(n * k)
Space Complexity: O(n + k)

import java.util.Arrays;

public class RadixSort {
    public static void radixSort(int[] arr) {
        int max = Arrays.stream(arr).max().getAsInt();
        for (int exp = 1; max / exp > 0; exp *= 10) {
            countingSort(arr, exp);
        }
    }

    public static void countingSort(int[] arr, int exp) {
        int n = arr.length;
        int[] output = new int[n];
        int[] count = new int[10];

        Arrays.fill(count, 0);

        for (int i = 0; i < n; i++) {
            count[(arr[i] / exp) % 10]++;
        }

        for (int i = 1; i < 10; i++) {
            count[i] += count[i - 1];
        }

        for (int i = n - 1; i >= 0; i--) {
            output[count[(arr[i] / exp) % 10] - 1] = arr[i];
            count[(arr[i] / exp) % 10]--;
        }

        System.arraycopy(output, 0, arr, 0, n);
    }

    public static void main(String[] args) {
        int[] arr = {170, 45, 75, 90, 802, 24, 2, 66};
        System.out.println("Original array: " + Arrays.toString(arr));
        radixSort(arr);
        System.out.println("Sorted array: " + Arrays.toString(arr));
    }
}

You can run each of these sorting algorithms independently to see how they work on different input arrays.