合并排序不排序数组

Question

I have written the Java code below after reading up on merge sort. There are no errors when running the code but the merge sort does not sort the array. It just returns the original unsorted array. I can't for the life of me figure out where the problem might be. I appreciate any leads.

public class mergeSort {

public void mergeSort(int array[], int n){

    if(n<2) return; 
    int m=n/2;
    int left[]=new int[m];
    int right[]=new int[n-m];
    int i;

    for(i=0; i<m;i++){
        left[i]=array[i];
    }
    for( i=m; i<n;i++){
        right[i-m]=array[i];
    }
    printArray(left);
    printArray(right);
    mergeSort(left, m);
    mergeSort(right, n-m);
    merge(array, left, m, right, m-n);
}

private void merge(int[] array, int[] left, int leftCount, int[] right, int rightCount) {
    int i=0,j=0,k=0;

    while(i<leftCount && j< rightCount){
        if(left[i]<=right[j]){
            array[k]=left[i];
            i++;
            k++;
        }else{
            array[k]=right[j];
            j++;
            k++;
        }
    }

    while(i<leftCount){
        array[k]=left[i];
        i++;
        k++;
    }
    while(j<rightCount){
        array[k]=right[j];
        j++;
        k++;
    }

}
 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 a[]={3,2,1,7,9,8};
    printArray(a);


    mergeSort m=new mergeSort();
    m.mergeSort(a, a.length);

    printArray(a);
}

}

Answer 1

The leftCount and rightCount that you pass to the merge method is wrong.

Instead don't pass that but calculate that in the merge method. I tried your code with the below change and it works perfectly fine.

 merge(array, left, right);
 ...
private void merge(int[] array, int[] left,  int[] right) {
    int i=0,j=0,k=0;
    int leftCount= left.length;
    int rightCount = right.length;