Using insertion sort to sort only part of array

Question

I'm writing a quicksort program. Part of the quicksort involves using insertionsort, but it only sorts a certain range of elements, since quicksort handles the rest. I'm trying to emulate a method provided by my textbook that uses

   public static void insertionSort(int a[], int left, int right)

But I am struggling to figure out how left and right are used. Here is the insertionsort code without using the parameters left and right:

public static void insertionSort(int a[], int left, int right) {
    int j;
    for (int p = 1; p < a.length; p++) {
        int tmp = a[p];
        for(j = p; j > 0 && tmp < a[j - 1]; j--) {
            a[j] = a[j-1];
        }
        a[j] = tmp;
    }
}

If I were to add the left and right parameters to help sort only part of the array, where would they apply?

Thanks for the help.

Answer 1

Use left and right in the for loop declaration:

public static void insertionSort(int a[], int left, int right) {
    int j;
    for (int p = left; p < right; p++) {
        int tmp = a[p];
        for(j = p; j > 0 && tmp < a[j - 1]; j--) {
            a[j] = a[j-1];
        }
        a[j] = tmp;
    }
}

example input: insertionSort({3, 2, 6, 5, 8, 3, 6, 7, 0}, 2, 6)

example output: {3, 2, 3, 5, 6, 8, 6, 7, 0}

edit:

In the above example, left is inclusive and right is exclusive. If you want to include the right index, change p < right to p<= right. Keep in mind when calling the method that indexing starts at 0.