mergeSort.cpp

/*
* @author : imkaka
* @date   : 5/2/2019
*/

#include<iostream>
#include<vector>

using namespace std;

// Merges two subarrays of arr[].
void merge(vector<int>& arr, int l, int m, int r)
{
    int i, j, k;
    int n1 = m - l + 1;
    int n2 =  r - m;

    //create temp arrays
    int L[n1], R[n2];

    //Copy data to temp arrays L[] and R[]
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1+ j];

    // Merge the temp arrays back
    i = 0; // Initial index of first subarray
    j = 0; // Initial index of second subarray
    k = l; // Initial index of merged subarray
    while (i < n1 && j < n2)
    {
        if (L[i] <= R[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    // Copy the remaining elements of L[]
    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }

    //Copy the remaining elements of R[]
    while (j < n2)
    {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(vector<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 print(const vector<int>& arr){
    for(const int x : arr){
        cout << x << " ";
    }

    cout << endl;
}
int main(){
    vector<int> arr = {12, 34, 1, -5, 10, 43, 23, 100, 100000, 0};

    cout << "Before Sorting : ";
    print(arr);

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

    cout << endl << "After Sorting : ";
    print(arr);
    return 0;
}