MergeSort.java

class MergeSort {
    private static void merge(int arr[], int l, int m, int r) {
        int n1 = m - l + 1;
        int n2 = r - m;

        int L[] = new int [n1];
        int R[] = new int [n2];

        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];
        }

        int i = 0, j = 0;
        int k = l;
        while (i < n1 && j < n2) {
            if (L[i] <= R[j]) {
                arr[k] = L[i];
                i++;
            }
            else {
                arr[k] = R[j];
                j++;
            }
            k++;
        }

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

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

    private static void sort(int arr[], int l, int r) {
        if (l < r) {
            int m = (l+r)/2;

            sort(arr, l, m);
            sort(arr , m+1, r);
            merge(arr, l, m, r);
        }
    }

    public static void main(String args[]) {
        int arr[] = {64, 25, 12, 22, 11};

        System.out.println("Original Array");
        for (Integer i : arr) {
            System.out.print(i + " ");
        }
        System.out.println("\n");
        sort(arr, 0, arr.length-1);
        System.out.println("Sorted array");
        for (Integer i : arr) {
            System.out.print(i + " ");
        }
        System.out.println();
    } 
}