MergeSort.java

import java.util.Arrays;

class MergeSort {

  void merge(int array[], int p, int q, int r) {

    int n1 = q - p + 1;
    int n2 = r - q;

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

    for (int i = 0; i < n1; i++)
      L[i] = array[p + i];
    for (int j = 0; j < n2; j++)
      M[j] = array[q + 1 + j];

    int i, j, k;
    i = 0;
    j = 0;
    k = p;

    while (i < n1 && j < n2) {
      if (L[i] <= M[j]) {
        array[k] = L[i];
        i++;
      } else {
        array[k] = M[j];
        j++;
      }
      k++;
    }
    
    while (i < n1) {
      array[k] = L[i];
      i++;
      k++;
    }

    while (j < n2) {
      array[k] = M[j];
      j++;
      k++;
    }
  }

  void mergeSort(int array[], int left, int right) {
    if (left < right) {

      int mid = (left + right) / 2;

      mergeSort(array, left, mid);
      mergeSort(array, mid + 1, right);

      merge(array, left, mid, right);
    }
  }

  public static void main(String args[]) {

    int[] array = { 6, 5, 12, 10, 9, 1 };

    MergeSort ob = new MergeSort();

    ob.mergeSort(array, 0, array.length - 1);

    System.out.println("Sorted Array:");
    System.out.println(Arrays.toString(array));
  }
}