Merge Sort Lesson Hacks
public class MergeSort {
static void sort(String arr[], int l, int r)
{
if (l < r) {
// COMMENT A
int m = l + (r - l) / 2;
// COMMENT B
sort(arr, l, m);
sort(arr, m + 1, r);
// COMMENT C
merge(arr, l, m, r);
}
}
static void merge(String arr[], int l, int m, int r)
{
// Find the sizes of two subarrays to be merged
int n1 = m - l + 1;
int n2 = r - m;
/* Create temp arrays */
String[] L = new String[n1];
String[] R = new String[n2];
/* Copy data to temp arrays */
for (int i = 0; i < n1; ++i)
L[i] = arr[l + i];
for (int j = 0; j < n2; ++j)
R[j] = arr[m + 1 + j];
/* Merge the temp arrays */
// Initial indexes of first and second subarrays
int i = 0, j = 0;
// Initial index of merged subarray array
int k = l;
while (i < n1 && j < n2) {
if (L[i].compareTo(R[j]) < 0) {
arr[k] = L[i];
i++;
}
else {
arr[k] = R[j];
j++;
}
k++;
}
/* Copy remaining elements of L[] if any */
while (i < n1) {
arr[k] = L[i];
i++;
k++;
}
/* Copy remaining elements of R[] if any */
while (j < n2) {
arr[k] = R[j];
j++;
k++;
}
}
public static void main(String[] args) {
// testing
String[] arr = { "c", "a", "e", "b", "d" };
int n = arr.length;
sort(arr, 0, n - 1);
System.out.println(Arrays.toString(arr));
}
}
MergeSort.main(null);
public class MergeSortAny {
// uses comparable as a generic type, as long as the type implements comparable
// any primitive will work as well as any object that implements comparable
static void sort(Comparable arr[], int l, int r)
{
if (l < r) {
// COMMENT A
int m = l + (r - l) / 2;
// COMMENT B
sort(arr, l, m);
sort(arr, m + 1, r);
// COMMENT C
merge(arr, l, m, r);
}
}
static void merge(Comparable arr[], int l, int m, int r)
{
// Find the sizes of two subarrays to be merged
int n1 = m - l + 1;
int n2 = r - m;
/* Create temp arrays */
Comparable[] L = new Comparable[n1];
Comparable[] R = new Comparable[n2];
/* Copy data to temp arrays */
for (int i = 0; i < n1; ++i)
L[i] = arr[l + i];
for (int j = 0; j < n2; ++j)
R[j] = arr[m + 1 + j];
/* Merge the temp arrays */
// Initial indexes of first and second subarrays
int i = 0, j = 0;
// Initial index of merged subarray array
int k = l;
while (i < n1 && j < n2) {
if (L[i].compareTo(R[j]) < 0) {
arr[k] = L[i];
i++;
}
else {
arr[k] = R[j];
j++;
}
k++;
}
/* Copy remaining elements of L[] if any */
while (i < n1) {
arr[k] = L[i];
i++;
k++;
}
/* Copy remaining elements of R[] if any */
while (j < n2) {
arr[k] = R[j];
j++;
k++;
}
}
public static void main(String[] args) {
// testing
Integer[] arr = { 3, 1, 5, 2, 4 };
int n = arr.length;
sort(arr, 0, n - 1);
System.out.println(Arrays.toString(arr));
}
}
MergeSortAny.main(null);
As seen above, the merge sort algorithm is not limited to integers, being now able to perform for any datatye that has the comparable interface.