Notes

/* C program for Merge Sort */
#include<stdlib.h>
#include<stdio.h>
#include<time.h>

// 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);
}
}

void merge2(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++;
}
}

void mergeSortdesc(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
mergeSortdesc(arr, l, m);
mergeSortdesc(arr, m+1, r);

merge2(arr, l, m, r);
}
}

/* UTILITY FUNCTIONS */
/* Function to print an array */
void printArray(int A[], int size)
{
int i;
for (i=0; i < size; i++)
printf("%d ", A[i]);
printf("n");
}

/* Driver program to test above functions */
int main()
{ clock_t start,end;
double CPU_time;
int d,i,arr[6],arr_size;





while(d!=6 && d>=1)
{
printf("ntArray will be generated");
for(i=0;i<5;i++){
arr[i]=rand();
}

arr_size = sizeof(arr)/sizeof(arr[0]);

printf("nGenerated array is n");
printArray(arr, arr_size);

printf("nOptionsnt1. Sort array in ascnt2. Sort array in descnt3. Best Casent4. Worst Casent5. Average Casent6. QuitnntChoice : ");
scanf("%d",&d);



switch(d){

case 1: start=clock();
mergeSort(arr, 0, arr_size-1);
end=clock();
CPU_time= ((double)(end-start))/CLOCKS_PER_SEC;
printf("nntSorted array is n");
printArray(arr, arr_size);
printf("ntTime taken:%fnn",CPU_time);
break;
case 2: start=clock();
mergeSortdesc(arr, 0, arr_size-1);
end=clock();
CPU_time= ((double)(end-start))/CLOCKS_PER_SEC;
printf("nntSorted array is n");
printArray(arr, arr_size);
printf("ntTime taken:%fnn",CPU_time);
break;
case 3: start=clock();
mergeSort(arr, 0, arr_size-1);
mergeSort(arr, 0, arr_size-1);
end=clock();
CPU_time= ((double)(end-start))/CLOCKS_PER_SEC;
printf("nntSorted array is n");
printArray(arr, arr_size);
printf("ntTime taken:%fnn",CPU_time);
break;
case 4: start=clock();
mergeSortdesc(arr, 0, arr_size-1);
mergeSort(arr, 0, arr_size-1);
end=clock();
CPU_time= ((double)(end-start))/CLOCKS_PER_SEC;
printf("nntSorted array is n");
printArray(arr, arr_size);
printf("ntTime taken:%fnn",CPU_time);
break;
case 5: start=clock();
mergeSort(arr, 0, arr_size-1);
end=clock();
CPU_time= ((double)(end-start))/CLOCKS_PER_SEC;
printf("nntSorted array is n");
printArray(arr, arr_size);
printf("ntTime taken:%fnn",CPU_time);
break;
case 6: break;
default: printf("wrong choixce");
}
}


return 0;
}