Question

1. rite a C++ program that implements the merge sort recursive algorithm. For simplicity you may hard-code the list of elements to order. Additionally, you may order elements in increasing or decreasing order, your call. Sample Output Elements to so 8 2 4 69 7 10 1 5 3 Results using merge sort 1 2 3 4 5 6 7 8 9 10

Here's my code in C++ so far. I don't understand how to split the array into subarrays then sort each subarray to merge into a final sorted array

Answer 1

HI, Please find my implementation.

Please let me know in case of any issue.

#include <iostream>
using namespace std;

// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge(int arr[], int l, int m, int r)
{
int i, j, k;
int n1 = m - l + 1;
int n2 = r - m;

/* create temp arrays */
int L[n1], R[n2];

/* Copy data to temp arrays L[] and R[] */
for (i = 0; i < n1; i++)
L[i] = arr[l + i];
for (j = 0; j < n2; j++)
R[j] = arr[m + 1+ j];

/* Merge the temp arrays back into arr[l..r]*/
i = 0; // Initial index of first subarray
j = 0; // Initial index of second subarray
k = l; // Initial index of merged subarray
while (i < n1 && j < n2)
{
if (L[i] <= R[j])
{
arr[k] = L[i];
i++;
}
else
{
arr[k] = R[j];
j++;
}
k++;
}

/* Copy the remaining elements of L[], if there
are any */
while (i < n1)
{
arr[k] = L[i];
i++;
k++;
}

/* Copy the remaining elements of R[], if there
are any */
while (j < n2)
{
arr[k] = R[j];
j++;
k++;
}
}

/* l is for left index and r is right index of the
sub-array of arr to be sorted */
void mergeSort(int arr[], int l, int r)
{
if (l < r)
{
// Same as (l+r)/2, but avoids overflow for
// large l and h
int m = l+(r-l)/2;

// Sort first and second halves
mergeSort(arr, l, m);
mergeSort(arr, m+1, r);

merge(arr, l, m, r);
}
}

/* Function to print an array */
void displayElement(int A[], int size)
{
for (int i=0; i < size; i++)
cout<<A[i]<<" ";
cout<<endl;
}

/* Driver program to test above functions */
int main()
{
int arr[] = {8,2,4,6,9,7,10,1,5,3};
int arr_size = 10;

cout<<"Elements to sort: "<<endl;;
displayElement(arr, arr_size);

mergeSort(arr, 0, arr_size - 1);

cout<<"\nResult using merge sort: "<<endl;;
displayElement(arr, arr_size);
return 0;
}