Merge Sort

It is a sorting algorithm that follows the divide-and-conquer approach. It efficiently sorts an array or a list by dividing it into smaller sub-arrays, sorting them, and then merging them back together.

C++ Code

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

void merge(int array[], int const left, int const mid, int const right){
    int const subArrayOne = mid - left + 1;
    int const subArrayTwo = right - mid;
    auto *leftArray = new int[subArrayOne],
        *rightArray = new int[subArrayTwo];

    for (auto i = 0; i < subArrayOne; i++)
        leftArray[i] = array[left + i];
    for (auto j = 0; j < subArrayTwo; j++)
        rightArray[j] = array[mid + 1 + j];

    auto indexOfSubArrayOne = 0, indexOfSubArrayTwo = 0;
    int indexOfMergedArray = left;

    while (indexOfSubArrayOne < subArrayOne
        && indexOfSubArrayTwo < subArrayTwo) {
        if (leftArray[indexOfSubArrayOne]
            <= rightArray[indexOfSubArrayTwo]) {
            array[indexOfMergedArray]
                = leftArray[indexOfSubArrayOne];
            indexOfSubArrayOne++;
        }
        else {
            array[indexOfMergedArray]
                = rightArray[indexOfSubArrayTwo];
            indexOfSubArrayTwo++;
        }
        indexOfMergedArray++;
    }

    while (indexOfSubArrayOne < subArrayOne) {
        array[indexOfMergedArray]
            = leftArray[indexOfSubArrayOne];
        indexOfSubArrayOne++;
        indexOfMergedArray++;
    }

    while (indexOfSubArrayTwo < subArrayTwo) {
        array[indexOfMergedArray]
            = rightArray[indexOfSubArrayTwo];
        indexOfSubArrayTwo++;
        indexOfMergedArray++;
    }
    delete[] leftArray;
    delete[] rightArray;
}

void mergeSort(int array[], int const begin, int const end)
{
    if (begin >= end)
        return;

    int mid = begin + (end - begin) / 2;
    mergeSort(array, begin, mid);
    mergeSort(array, mid + 1, end);
    merge(array, begin, mid, end);
}

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

int main()
{
    int arr[] = { 12, 11, 13, 5, 6, 7 };
    int arr_size = sizeof(arr) / sizeof(arr[0]);

    cout << "Given array is \n";
    printArray(arr, arr_size);

    mergeSort(arr, 0, arr_size - 1);

    cout << "\nSorted array is \n";
    printArray(arr, arr_size);
    return 0;
}

Comments

[Paul J. Lucas]

1. Headers in the bits subdirectory are for the implementation, not user code. Just include the correct headers.
2. You should at least use std::vector, not raw C++ arrays.
3. Your use of auto is inconsistent.

[Ankit Kumar Meena]

Thank You for the feedback. I'll keep these things in mind for my next post. I am actually learning C++, so that's why these small mistakes happen. I'll try to reduce these mistakes in the future.