Question

Please merge all the codes below and add comments using JAVA Program. I need a complete code which is the combination of the following codes:

// Merges the left/right elements into a sorted result.

// Precondition: left/right are sorted

public static void merge(int[] result, int[] left,

                                       int[] right) {

    int i1 = 0;   // index into left array

    int i2 = 0;   // index into right array

    for (int i = 0; i < result.length; i++) {

        if (i2 >= right.length ||

           (i1 < left.length && left[i1] <= right[i2])) {

            result[i] = left[i1];    // take from left

          i1++;

        } else {

            result[i] = right[i2];   // take from right

            i2++;

        }

    }

}

// Rearranges the elements of a into sorted order using

// the merge sort algorithm.

public static void mergeSort(int[] a) {

    // split array into two halves

    int[] left = Arrays.copyOfRange(a, 0, a.length/2);

    int[] right = Arrays.copyOfRange(a, a.length/2, a.length);

    // sort the two halves

    ...

    // merge the sorted halves into a sorted whole

    merge(a, left, right);

}

// Rearranges the elements of a into sorted order using

// the merge sort algorithm (recursive).

public static void mergeSort(int[] a) {

    if (a.length >= 2) {

        // split array into two halves

        int[] left = Arrays.copyOfRange(a, 0, a.length/2);

        int[] right = Arrays.copyOfRange(a, a.length/2, a.length);

        // sort the two halves

        mergeSort(left);

        mergeSort(right);

        // merge the sorted halves into a sorted whole

        merge(a, left, right);

    }

}

Answer 1

Here, your first function and third function completes MergeSort solution, second function is irrelevant in this code.

The complete answer for this question is as below:

public static void merge(int[] result, int[] left,int[] right) {

       int i1 = 0; // index into left array

       int i2 = 0; // index into right array

       for (int i = 0; i < result.length; i++) {

           if (i2 >= right.length ||

           (i1 < left.length && left[i1] <= right[i2])) {

               result[i] = left[i1]; // take from left

               i1++;

           } else {

               result[i] = right[i2]; // take from right

               i2++;

           }

       }

   }

   // Rearranges the elements of a into sorted order using

   // the merge sort algorithm (recursive).

   public static void mergeSort(int[] a) {

       if (a.length >= 2) {

           // split array into two halves

           int[] left = Arrays.copyOfRange(a, 0, a.length / 2);

           int[] right = Arrays.copyOfRange(a, a.length / 2, a.length);

           // sort the two halves

           mergeSort(left);

           mergeSort(right);

           // merge the sorted halves into a sorted whole

           merge(a, left, right);

       }

   }