MergeSort.cpp

#include <iostream>
using namespace std;

void merge(int arr[], int p, int q, int r)
{

    int n1 = q - p + 1;
    int n2 = r - q;

    int L[n1], M[n2];

    for (int i = 0; i < n1; i++)
        L[i] = arr[p + i];
    for (int j = 0; j < n2; j++)
        M[j] = arr[q + 1 + j];

    int i, j, k;
    i = 0;
    j = 0;
    k = p;

    while (i < n1 && j < n2)
    {
        if (L[i] <= M[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = M[j];
            j++;
        }
        k++;
    }

    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }

    while (j < n2)
    {
        arr[k] = M[j];
        j++;
        k++;
    }
}

void mergeSort(int arr[], int l, int r)
{
    if (l < r)
    {
        int m = l + (r - l) / 2;

        mergeSort(arr, l, m);
        mergeSort(arr, m + 1, r);

        merge(arr, l, m, r);
    }
}

void printArray(int arr[], int size)
{
    for (int i = 0; i < size; i++)
        cout << arr[i] << " ";
    cout << endl;
}

int main()
{
    int a[50], size, i;
    cout << "----------------------------------";
    cout << "\nMerge Sort" << endl;
    cout << "\nEnter the number of elements: ";
    cin >> size;
    cout << "\nEnter array elements: ";

    for (i = 0; i < size; i++)
        cin >> a[i];
    cout << "\nArray before sorting: ";

    for (i = 0; i < size; i++)
        cout << a[i] << " ";
    ;

    mergeSort(a, 0, size - 1);

    cout << "\nSorted array: ";
    printArray(a, size);
    return 0;
}