merge sort

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

vector <int> merge(vector <int>left, vector <int>right)
{
    int leftSz = left.size();
    int rightSz = right.size();
    vector <int> sortedArr(leftSz+rightSz);
    int l = 0, r = 0, index = 0;
    while(l < leftSz && r < rightSz)
    {
        if(left[l] <= right[r])
        {
            sortedArr[index] = left[l];
            l++;
        }
        else
        {
            sortedArr[index] = right[r];
            r++;
        }
        index++;
    }


    while(l<leftSz)
    {
        sortedArr[index]=left[l];
        l++;
        index++;
    }
    while(r<rightSz)
    {
        sortedArr[index]=right[r];
        r++;
        index++;
    }
    return sortedArr;
}

void printVector(vector <int> numbers)
{
    int size=numbers.size();
    for(int i=0; i<size; i++) cout<<numbers[i]<<" ";
    cout<<endl;
}


vector <int> mergeSOrt(vector <int> numbers)
{
    int l=0, h=numbers.size()-1;
    if(l!=h)
    {
        int m=h/2;
        vector <int>left, right;
        for(int i=0; i<=m; i++) left.push_back(numbers[i]);
        for(int i=m+1; i<=h; i++) right.push_back(numbers[i]);
        left=mergeSOrt(left);
        right=mergeSOrt(right);
        numbers=merge(left, right);
    }
    return numbers;
}

int main()
{
    vector <int>numbers;
    numbers.clear();

    int sz = 500000;
    for(int i=1; i<=sz; i++)
    {
        int n = rand();
        numbers.push_back(n);
    }
    std::clock_t start;
    double duration;

    start = std::clock();

    numbers=mergeSOrt(numbers);
    duration = ( std::clock() - start ) / (double) CLOCKS_PER_SEC;

    cout<<duration*1000.0<<endl;

    return 0;
}