Quicksort in C++

quicksort.cpp

#include <vector>
#include <stack>

int partition(std::vector<int>& input, int left, int right)
{
    if (left < right)
    {
        int pivotValue = input[right];
        // This represent the current position of the pivot
        int pivotIndex = left;
        for (int index = pivotIndex; index < right; ++index)
        {
            if (input[index] <= pivotValue)
            {
                // We swap the current value with the one in the pivot position
                // increment the pivot index
                std::swap(input[index], input[pivotIndex++]);
            }
        }
        // Finally swap the pivot value which is at the right of the array with the value in the pivot index.
        // Which should be >= to the pivot value
        std::swap(input[pivotIndex], input[right]);
        return pivotIndex;
    }
    return -1;
}

void quickSortRec(std::vector<int>& input, int l, int r)
{
    if (l < r)
    {
        int j = partition(input, l, r);
        quickSortRec(input, l, j - 1);
        quickSortRec(input, j + 1, r);
    }
}

#define USE_RECURSIVE 0
void quickSort(std::vector<int>& input)
{
#if USE_RECURSIVE
    quickSortRec(input, 0, input.size() - 1);
#else
    // we just use a stack for the iterative version. 
    // this will just simulate the stack of recursion.
    std::stack<int> stack;
    stack.push(0);
    stack.push(input.size() - 1);

    while (!stack.empty())
    {
        int right = stack.top();
        stack.pop();
        int left = stack.top();
        stack.pop();
        if (left < right)
        {
            int pivotIndex = partition(input, left, right);
            if (left < pivotIndex - 1)
            {
                stack.push(left);
                stack.push(pivotIndex - 1);
            }
            if (right > pivotIndex + 1)
            {
                stack.push(pivotIndex + 1);
                stack.push(right);
            }
        }
    }
#endif
}

int main()
{
    std::vector<int> test1 = { 6, 3, 7, 5, 1, 2 };
    std::vector<int> test2 = { 33, 34, 212, -321, 4, 4 ,2, 1 };
    std::vector<int> test3 = { 9, 2, 1, 4893, 2, 43, -1 };
    quickSort(test1);
    quickSort(test2);
    quickSort(test3);
    return 0;
}