Following is a typical recursive implementation of Merge Sort that uses last element as pivot.
C
/* Recursive C program for merge sort */ #include <stdio.h> #include <stdlib.h> /* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */ void merge( int arr[], int l, int m, int r);
/* 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) {
int m = l + (r - l) / 2; // Same as (l+r)/2 but avoids overflow for large l & h
mergeSort(arr, l, m);
mergeSort(arr, m + 1, r);
merge(arr, l, m, r);
}
} /* Function to merge the two haves arr[l..m] and arr[m+1..r] of array arr[] */ 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;
j = 0;
k = l;
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++;
}
} /* 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()
{ int arr[] = { 12, 11, 13, 5, 6, 7 };
int arr_size = sizeof (arr) / sizeof (arr[0]);
printf ( "Given array is \n" );
printArray(arr, arr_size);
mergeSort(arr, 0, arr_size - 1);
printf ( "\nSorted array is \n" );
printArray(arr, arr_size);
return 0;
} |
Output:
Given array is 12 11 13 5 6 7 Sorted array is 5 6 7 11 12 13
Time Complexity: O(n*log(n))
Auxiliary Space: O(n)
Please refer complete article on Iterative Merge Sort for more details!