merge sort merge code example

Example 1: merge sort

//merge sort
#include <iostream>

using namespace std;
void merge(int arr[],int start,int mid,int end)
{
    int n1=mid-start+1;
    int n2=end-mid;
    int l[n1],m[n2];
    for(int i=0;i<n1;i++)
    {
        l[i]=arr[start+i];
    }
    for(int j=0;j<n2;j++)
    {
        m[j]=arr[mid+1+j];
    }
    int i=0;
    int j=0;
    int k=start;
    while(i<n1&&j<n2)
    {
        if(l[i]<m[j])
        {
            arr[k]=l[i];
            k++;
            i++;
        }
        else
        {
            arr[k]=m[j];
            k++;
            j++;
        }
    }
    while(i<n1)
    {
        arr[k]=l[i];
        k++;
        i++;
    }
    while(j<n2)
    {
        arr[k]=m[j];
        k++;
        j++;
    }
}
void mergesort(int arr[],int start,int end)
{
    if(start<end)
    {
        int mid=(start+end)/2;
        mergesort(arr,start,mid);
        mergesort(arr,mid+1,end);
        merge(arr,start,mid,end);
    }
}
void display(int arr[],int n)
{
    for(int i=0;i<n;i++)
    {
        cout<<arr[i]<<" ";
    }
    cout<<endl;
}

int main()
{
    int n;
    cout<<"enter the size of the array:"<<endl;
    cin>>n;
    cout<<"enter the elements of the array:"<<endl;
    int arr[n];
    for(int i=0;i<n;i++)
    {
        cin>>arr[i];
    }
    cout<<"array as it is:"<<endl;
    display(arr,n);
    cout<<"sorted array:"<<endl;
    mergesort(arr,0,n-1);
    display(arr,n);
    return 0;
}

Example 2: merge sort

# Python3 recursive merge sort algorithm -> O(n*log(n))
def merge_sort(A):
    def merge(l, r):
        i = j = 0
        n = []  # merging container
        while i < len(l) or j < len(r):

            # if no more elements to the right,
            # add remaining left elements
            if i == len(l):
                n.extend(r[j:])
                break

            # if no more elements to the left,
            # add remaining right elements
            if j == len(r):
                n.extend(l[i:])
                break

            # if elements left on both sides,
            # add smaller element
            a, b = l[i], r[j]
            if a < b:
                n.append(a)
                i += 1
            else:
                n.append(b)
                j += 1

        return n

    # divide list down to single-elements
    s = len(A)
    if s > 1:
        s //= 2
        l = merge_sort(A[:s])  # split left
        r = merge_sort(A[s:])  # split right
        return merge(l, r)  # merge sides in order
    else:
        return A