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# C Exercises: Merge sort algorithm

## C Programming Searching and Sorting Algorithm: Exercise-5 with Solution

Write a C program to sort a list of elements using the merge sort algorithm.
Note: Merge sort is an O(n log n) comparison-based sorting algorithm. Most implementations produce a stable sort, which means that the implementation preserves the input order of equal elements in the sorted output.

Pictorial presentation - Merge search algorithm :

Sample Solution:

Sample C Code:

``````#include<stdio.h>
/* Function to merge the two haves arra[l..m] and arra[m+1..r] of array arra[] */
void merge(int arra[], 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] = arra[l + i];
for(j = 0; j < n2; j++)
R[j] = arra[m + 1+ j];
i = 0;
j = 0;
k = l;
while (i < n1 && j < n2)
{
if (L[i] <= R[j])
{
arra[k] = L[i];
i++;
}
else
{
arra[k] = R[j];
j++;
}
k++;
}
while (i < n1)
{
arra[k] = L[i];
i++;
k++;
}
while (j < n2)
{
arra[k] = R[j];
j++;
k++;
}
}
void mergeSort(int arra[], int l, int r)
{
if (l < r)
{
int m = l+(r-l)/2; //Same as (l+r)/2, but avoids overflow for large l and h
mergeSort(arra, l, m);
mergeSort(arra, m+1, r);
merge(arra, l, m, r);
}
}
/* Function to print an array */
void print_array(int A[], int size)
{
int i;
for (i=0; i < size; i++)
printf("%d ", A[i]);
printf("\n");
}
/* Test above functions */
int main()
{
int arra[] = {125, 181, 130, 25, 61, 887};
int arr_size = sizeof(arra)/sizeof(arra[0]);
printf("Given array is \n");
print_array(arra, arr_size);
mergeSort(arra, 0, arr_size - 1);
printf("\nSorted array is \n");
print_array(arra, arr_size);
return 0;
}
```
```

Sample Output:

```Given array is
125 181 130 25 61 887

Sorted array is
25 61 125 130 181 887
```

Flowchart:

C Programming Code Editor:

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