Quick MergeSort troubleshooting [closed]

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I've been trying get my Mergesort method to work, but it's giving me some funky outputs.

// mergesort method
// recursively sorts the array by breaking into small sub-arrays and then merging
public static int[] mergeSort(int[] nums){
    int halfwayAndOne = (nums.length / 2);
    int a = 0, b = 0;
    if (nums.length <= 1)
        return nums;
    else{
        int[] l = new int[nums.length / 2];
        int[] r = new int[nums.length - l.length];
        for (int i = 0; i < l.length; i++)
            l[i] = nums[i];
        for (int j = 0; j < nums.length - l.length; j++){
            r[j] = nums[halfwayAndOne];
            halfwayAndOne++;
        }

        for (int n = 0; n < nums.length; n++){
            if (a < l.length && b < r.length) {
                if (l[a] < r[b]) {
                    nums[n] = l[a];
                    a++;
                } else {
                    nums[n] = r[b];
                    b++;
                }
            }

            else if (a == l.length)
                nums[n] = r[b];
            else
                nums[n] = l[a];
        }

        mergeSort(l);
        mergeSort(r);

        printArr(l);
        printArr(r);

        return nums;
    }
}

// method to print out the array
public static void printArr(int[] arr){
    System.out.println(Arrays.toString(arr));
}

This is the output:

[4, 0, 10, 15, 2, 1, 8, 9, 20, 3, 5]
[4]
[0]
[15]
[2]
[10]
[2, 15]
[0, 4]
[10, 15, 15]
[8]
[9]
[1]
[8, 9]
[3]
[5]
[20]
[3, 5]
[1, 8, 8]
[3, 5, 20]
[4, 0, 10, 10, 10]
[1, 8, 9, 20, 20, 20]
[1, 4, 0, 8, 9, 10, 15, 2, 20, 20, 20]

The first array is the original array, and the output should be sorted from least to greatest

Edit: My question is where is my program not working, thought it was self explanatory, sorry.

Answer 1

At the point where you merge l and r back in to nums, have l and r been sorted yet?