Generate code, for counting sort, without any function from other libraryes

#include <iostream>
#include <vector>

using std::cin;
using std::cout;
using std::vector;
using std::max;

void countSort(vector<int>& arr) {
    int n = arr.size();
    // The output character array that will have sorted arr
    vector<int> output(n);
    // Create a count array to store count of inidividul
    // characters and initialize count array as 0
    vector<int> count(1000, 0);

    // store count of each character
    for(int i=0; i<n; ++i)
        ++count[arr[i]];

    // Change count[i] so that count[i] now contains actual
    // position of this character in output array
    for (int i=1; i<=1000; ++i)
        count[i] += count[i-1];

    // Build the output character array
    for (int i = 0; i<n; ++i)
    {
        output[count[arr[i