MergeSort.java

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

            // Divide and sort both halves
            mergeSort(arr, left, mid);
            mergeSort(arr, mid + 1, right);

            // Merge the sorted halves
            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[] leftArray = new int[n1];
        int[] rightArray = new int[n2];

        for (int i = 0; i < n1; i++) leftArray[i] = arr[left + i];
        for (int j = 0; j < n2; j++) rightArray[j] = arr[mid + 1 + j];

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

        while (i < n1) arr[k++] = leftArray[i++];
        while (j < n2) arr[k++] = rightArray[j++];
    }

    public static void main(String[] args) {
        int[] numbers = {12, 11, 13, 5, 6};
        mergeSort(numbers, 0, numbers.length - 1);

        System.out.println("Sorted Array:");
        for (int num : numbers) {
            System.out.print(num + " ");
        }
    }
}