C++ QuickSort not sorting

Question

void quickSort(vector<double> unsortedData, int leftBound, int rightBound) {

    if (leftBound < rightBound) {
        double i = partitionStep(unsortedData, leftBound, rightBound);
        quickSort(unsortedData, leftBound, i-1);
        quickSort(unsortedData, i + 1, rightBound);
    }
}

double partitionStep(vector<double> unsortedData, int leftBound, int rightBound) {

    double pivot = unsortedData[rightBound];

    while (leftBound <= rightBound) {

        while ((unsortedData[leftBound] < pivot)) {
            leftBound++;
        }
        while ((unsortedData[rightBound] > pivot)) {
            rightBound--;
        }

        if (unsortedData[leftBound] == unsortedData[rightBound]) {
            leftBound++;
        } else if (leftBound < rightBound) {
            double temp = unsortedData[leftBound];
            unsortedData[leftBound] = unsortedData[rightBound];
            unsortedData[rightBound] = temp;
        }
    }

    return rightBound;
}

I need to sort a vector of doubles. This code runs but the vector is not sorted at the end. It's probably something that I am overlooking. Thoughts?

Answer 1

A high level description of your quickSort routine is:

• Take as input a copy of the original vector and the endpoints of a range
• Do stuff with the copy
• Discard the copy

which isn't particularly useful. Change the input argument to vector<double>& so that you're doing stuff with a reference to the original vector rather than a copy.