Merge Sort (using divide and conquer approach) in C++ with explaination!

#include<iostream>

#include<vector>

using namespace std;

// conquer step - O(n)

void merge(int arr[], int si, int mid,int ei) {  

    vector<int> temp;

    int i = si;

    int j = mid+1;

    while(i <= mid && j <= ei) {

        if(arr[i] <= arr[j]) { // so jo value choti hai, ushe add krna h

            temp.push_back(arr[i++]);

        } else {

            temp.push_back(arr[j++]);

        }

    }

    // i will keep pushing itself until reaches mid

    while(i <= mid) {

        temp.push_back(arr[i++]);

    }

    // j will keep pushing itself until reaches ei

    while(j <= ei) {

        temp.push_back(arr[j++]);

    }

    // vector -> original array

    for(int idx=si, x=0; idx <= ei; idx++)  { // playing this loop on original arr

        arr[idx] = temp[x++]; // temp ka iterater

    }

}

// merge sort step - O(nlogn)

void mergeSort(int arr[], int si, int ei) {

    if(si >= ei) {

        return;

    }

    int mid = si + (ei-si)/2;

    mergeSort(arr, si, mid); // left half

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

    merge(arr, si, mid, ei); // conquer

}

void printArr(int arr[], int n) {

    for(int i=0; i<n; i++) {

    cout << arr[i] << " ";

}

cout << endl;

}

int main() {

    int arr[6] = {6, 3, 7, 5, 2, 4};

    int n = 6;

    int si = 0;

    int ei = n-1;

    mergeSort(arr, si, ei);

    printArr(arr, n);

    return 0;

}