mergesort.cpp

#include <iostream>
#include <vector>

using namespace std;

// Merge function to combine two sorted halves
void merge(vector<int> &arr, int left, int mid, int right)
{
    int n1 = mid - left + 1;
    int n2 = right - mid;

    // Temporary arrays to hold the halves
    vector<int> leftArray(n1);
    vector<int> rightArray(n2);

    // Copy data to temporary arrays
    for (int i = 0; i < n1; ++i)
        leftArray[i] = arr[left + i];
    for (int j = 0; j < n2; ++j)
        rightArray[j] = arr[mid + 1 + j];

    // Merge the temporary arrays back into the main array
    int i = 0, j = 0, k = left;
    while (i < n1 && j < n2)
    {
        if (leftArray[i] <= rightArray[j])
        {
            arr[k] = leftArray[i];
            ++i;
        }
        else
        {
            arr[k] = rightArray[j];
            ++j;
        }
        ++k;
    }

    // Copy remaining elements of leftArray, if any
    while (i < n1)
    {
        arr[k] = leftArray[i];
        ++i;
        ++k;
    }

    // Copy remaining elements of rightArray, if any
    while (j < n2)
    {
        arr[k] = rightArray[j];
        ++j;
        ++k;
    }
}

// Recursive Merge Sort function
void mergeSort(vector<int> &arr, int left, int right)
{
    if (left < right)
    {
        int mid = left + (right - left) / 2;

        // Sort the left half
        mergeSort(arr, left, mid);

        // Sort the right half
        mergeSort(arr, mid + 1, right);

        // Merge the sorted halves
        merge(arr, left, mid, right);
    }
}

int main()
{
    vector<int> arr = {38, 27, 43, 3, 9, 82, 10};

    cout << "Original array: ";
    for (int num : arr)
        cout << num << " ";
    cout << endl;

    mergeSort(arr, 0, arr.size() - 1);

    cout << "Sorted array: ";
    for (int num : arr)
        cout << num << " ";
    cout << endl;

    return 0;
}