mergesort.java

   
public class MergeSort {

    void merge(int arr[], int low, int mid, int up) {
        int n1 = mid - low + 1;
        int n2 = up - mid;

        int Left[] = new int[n1];
        int Right[] = new int[n2];

        for (int i = 0; i < n1; ++i) {
            Left[i] = arr[low + i];
        }
        for (int j = 0; j < n2; ++j) {
            Right[j] = arr[mid + 1 + j];
        }

        int i = 0, j = 0;

        int k = low;
        while (i < n1 && j < n2) {
            if (Left[i] <= Right[j]) {
                arr[k] = Left[i];
                i++;
            } else {
                arr[k] = Right[j];
                j++;
            }
            k++;
        }

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

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

    void sort(int arr[], int low, int up) {
        if (low < up) {

            int mid = low + (up - low) / 2;

            sort(arr, low, mid);
            sort(arr, mid + 1, up);

            merge(arr, low, mid, up);
        }
    }

    static void printArray(int arr[]) {
        int n = arr.length;
        for (int i = 0; i < n; ++i) {
            System.out.print(arr[i] + " ");
        }
        System.out.println();
    }

    public static void main(String args[]) {
        int arr[] = {5, 75,85,81,92,25, 9, 6, 1, 4, 2, 8, 7};

        System.out.println("Given Array");
        printArray(arr);

        MergeSort ob = new MergeSort();
        ob.sort(arr, 0, arr.length - 1);

        System.out.println("\nSorted array");
        printArray(arr);
    }
}