MergeSort.java

public class MergeSort {

    static void merge(int[] arr,int l,int mid,int r)
    {
        System.out.println("l3 is "+l+" r3 is "+r+" "+mid);
        int n1=mid-l+1;
        System.out.println("n1 "+n1);
        int n2=r-mid;
        int[] a=new int[n1];
        int[] b=new int[n2];
        for(int i=0;i<n1;i++)
        {
            a[i]=arr[l+i];
        }
        for(int i=0;i<n2;i++)
        {
            b[i]=arr[mid+1+i];
        }

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

    }

    static void mergesort(int[] arr,int l,int r)
    {
        if(l<r) {
            int mid = (l + r) / 2;
            mergesort(arr, l, mid);
            mergesort(arr, mid + 1, r);

            merge(arr, l, mid, r);
        }
    }
    public static void main(String[] args)
    {
        int[] arr={2,5,1,5,7,9,2};
        mergesort(arr,0,arr.length-1);
        for(int i:arr)
        {
            System.out.println(i);
        }
    }
}