mergesort.cpp

#include <stdio.h>
//#include <stdlib.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;
    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++;
    }
}
 
// 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)//mergeSort(arr, 0, arr_size - 1);
{
    if (l < r) {//arr[0]=2, l=0; r=arr_size-1=6-1=5
        int m = l + ( r - l) / 2;//m=0+(5-0)/2
 
        // Sort first and second halves
        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);
 
        merge(arr, l, m, r);
    }
}
 
// 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 code
int main()
{
   int n,i, j;
	printf("Enter no of elements in the array:");
	scanf("%d",&n);
	int arr[n];
	printf("Enter array to be sorted:\n");
	for(i=0;i<n;i++)                   
	{
		scanf("%d",&arr[i]);
	}
 
    mergeSort(arr, 0, n - 1);
 
    printf("\nSorted array is \n");
    printArray(arr, n);
    return 0;
}