At every recursive step, print out to the console what the two halves are that a
ID: 3833921 • Letter: A
Question
At every recursive step, print out to the console what the two halves are that are going to be merged together.
public class Mergesort
{
private int[] numbers;
private int[] helper;
private int number;
public void sort(int[] values)
{
this.numbers = values;
number = values.length;
this.helper = new int[number];
System.out.println("START");
mergesort(0, number - 1);
System.out.println("END");
}
private void mergesort(int low, int high)
{
// Check if low is smaller then high, if not then the array is sorted
if (low < high)
{
// Get the index of the element which is in the middle
int middle = (low + high) / 2;
// Sort the left side of the array
mergesort(low, middle);
// Sort the right side of the array
mergesort(middle + 1, high);
// Combine them both
merge(low, middle, high);
}
}
private void merge(int low, int middle, int high)
{
// Copy both parts into the helper array
for (int i = low; i <= high; i++)
{
helper[i] = numbers[i];
}
int i = low;
int j = middle + 1;
int k = low;
// Copy the smallest values from either the left or the right side back
// to the original array
while (i <= middle && j <= high)
{
if (helper[i] <= helper[j])
{
numbers[k] = helper[i];
i++;
}
else
{
numbers[k] = helper[j];
j++;
}
k++;
}
// Copy the rest of the left side of the array into the target array
while (i <= middle)
{
numbers[k] = helper[i];
k++;
i++;
}
}
private void printArray()
{
for(int x : numbers)
System.out.print(x + " ");
System.out.println(" ");
}
}
Explanation / Answer
public class Mergesort
{
private int[] numbers;
private int[] helper;
private int number;
public void sort(int[] values)
{
this.numbers = values;
number = values.length;
this.helper = new int[number];
System.out.println("START");
mergesort(0, number - 1);
System.out.println("END");
}
private void mergesort(int low, int high)
{
// Check if low is smaller then high, if not then the array is sorted
if (low < high)
{
// Get the index of the element which is in the middle
int middle = (low + high) / 2;
// Sort the left side of the array
mergesort(low, middle);
// Sort the right side of the array
mergesort(middle + 1, high);
// Combine them both
merge(low, middle, high);
}
}
private void merge(int low, int middle, int high)
{
//printing left half and right half
System.out.println("Laft Half");//printing left half
for(int i=0;i<middle;i++)//left half starts from low to middle
{
System.out.println(numbers[i]+" ");
}
System.out.println(" ");
System.out.println("Right Half");//printing right half
for(int i=middle+1;i<high;i++)//right half starts from middle+1 to high
{
System.out.println(numbers[i]+" ");
}
System.out.println(" ");
// Copy both parts into the helper array
for (int i = low; i <= high; i++)
{
helper[i] = numbers[i];
}
int i = low;
int j = middle + 1;
int k = low;
// Copy the smallest values from either the left or the right side back
// to the original array
while (i <= middle && j <= high)
{
if (helper[i] <= helper[j])
{
numbers[k] = helper[i];
i++;
}
else
{
numbers[k] = helper[j];
j++;
}
k++;
}
// Copy the rest of the left side of the array into the target array
while (i <= middle)
{
numbers[k] = helper[i];
k++;
i++;
}
}
private void printArray()
{
for(int x : numbers)
System.out.print(x + " ");
System.out.println(" ");
}
}
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