Merge sort divide conquer


#1

Given n elements merge them into one sorted list using merge procedure?


#2

/* C program for Merge Sort */
#include<stdlib.h>
#include<stdio.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);
}

}

/* 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()
{
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;

}