Merge_Sort.cpp

#include <bits/stdc++.h>
using namespace std;

void merge(int arr[], int l, int mid, int r)
{
    int n1 = mid - l + 1;
    int n2 = r - mid;

    int a[n1];
    int b[n2]; // temp arrays

    for (int i = 0; i < n1; i++)
    {
        a[i] = arr[l + i];
    }
    for (int i = 0; i < n2; i++)
    {
        b[i] = arr[mid + i + 1];
    }

    int i = 0;
    int j = 0;
    int k = l;
    while (i < n1 && j < n2)
    {
        if (a[i] < b[j])
        {
            arr[k] = a[i];
            k++;
            i++;
        }
        else
        {
            arr[k] = b[j];
            k++;
            j++;
        }
    }

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

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

void mergeSort(int arr[], int l, int r)
{
    if (l < r)
    {
        int mid = (l + r) / 2;
        mergeSort(arr, l, mid);
        mergeSort(arr, mid + 1, r);

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

int main()
{
    int n;
    cout << "Enter the size of array: ";
    cin >> n;
    int arr[n];
    cout << "Enter the elements of array:\n";
    for (int i = 0; i < n; i++)
    {
        cin >> arr[i];
    }
    mergeSort(arr, 0, n - 1);

    cout << "Sorted Array is:\n";
    for (int i = 0; i < n; i++)
    {
        cout << arr[i] << " ";
    }
}

// Time COmplexity is O(n*log n);