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three_way_merge_sort.c
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three_way_merge_sort.c
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// C program to implement Three Way Merge Sort
#include <stdio.h>
// Time Complexity: O(n*logn)
// Space Complexity: O(n)
// Merge the three sections in ascending order
void merge(int arr[], int beg, int midA, int midB, int end, int temp[])
{
int i, j, k, l;
i = beg;
j = midA;
k = midB;
l = beg;
// Find the smallest element among the three sections
while ((i < midA) && (j < midB) && (k < end))
{
if(arr[i] < arr[j])
{
if(arr[i] < arr[k])
{
temp[l++] = arr[i++];
}
else
{
temp[l++] = arr[k++];
}
}
else
{
if(arr[j] < arr[k])
{
temp[l++] = arr[j++];
}
else
{
temp[l++] = arr[k++];
}
}
}
/*
Now any two arrays would have remaining values that are yet to be merged,
We have to identify those two arrays and merge the elements.
*/
while ((i < midA) && (j < midB))
{
if(arr[i] < arr[j])
{
temp[l++] = arr[i++];
}
else
{
temp[l++] = arr[j++];
}
}
while ((j < midB) && (k < end))
{
if(arr[j] < arr[k])
{
temp[l++] = arr[j++];
}
else
{
temp[l++] = arr[k++];
}
}
while ((i < midA) && (k < end))
{
if(arr[i] < arr[k])
{
temp[l++] = arr[i++];
}
else
{
temp[l++] = arr[k++];
}
}
/*
Now a single array would have remaining values that are yet to be merged,
We have identify that array and copy its remaining elements.
*/
while (i < midA)
temp[l++] = arr[i++];
while (j < midB)
temp[l++] = arr[j++];
while (k < end)
temp[l++] = arr[k++];
}
void three_way_merge_sort(int arr[], int beg, int end, int temp[])
{
//If the array contains only a single element, then return
if (end - beg < 2)
return;
// Split the array into three parts
int midA = beg + ((end - beg) / 3);
int midB = beg + 2 * ((end - beg) / 3) + 1;
three_way_merge_sort(temp, beg, midA, arr);
three_way_merge_sort(temp, midA, midB, arr);
three_way_merge_sort(temp, midB, end, arr);
// Merge the sorted arrays
merge(temp, beg, midA, midB, end, arr);
}
int main()
{
int n;
printf("\nHow many numbers do you want to sort? ");
scanf("%d",&n);
int arr[n];
if (n <= 0)
{
printf("There are no numbers to sort!!!");
return 0;
}
// Input the numbers to sort
printf("Enter the numbers: ");
for (int i = 0; i < n; i++)
scanf("%d",&arr[i]);
// creating a temporary array
int temp[n];
// Copy the elements of the temporary elements into the new array
for (int i = 0; i < n; i++)
temp[i] = arr[i];
//Call the sort function
three_way_merge_sort(temp, 0, n, arr);
printf("The numbers in sorted order is: ");
// Print the sorted array
for (int i = 0; i < n; i++)
printf(" %d ", temp[i]);
printf("\n");
return 0;
}
/*
SAMPLE INPUT AND OUTPUT
SAMPLE 1
How many numbers do you want to sort? 5
Enter the numbers: 1 3 5 2 4
The numbers in sorted order is: 1 2 3 4 5
SAMPLE 2
How many numbers do you want to sort? 0
There are no numbers to sort!!!
*/