Quicksort won't sort more than 50 elements

Asked May 06 '14 at 19:32

Active May 06 '14 at 19:34

Viewed 115 times

Here's how I generate the numbers to be sorted.

vector<int> list;
for (i=0;i<50;i++) list.push_back(rand() %1000);

Here is my call in main

quickSort(list , 0, (list.size() -1 ));

here's the quicksort function

int pivot = left;
int temp = right;

if(left > right - 1)
    return;

while (left != right) {
    if (pivot == left){
        if (list[pivot] > list[right]) {
            //-------------------------
            std:swap(list, right, pivot);
            //-------------------------
            pivot = right;
            left++;
        }else{
            right--;
        }

    }else{
        if (list[pivot] < list[left]) {
            //-------------------------
              swap(list, left, pivot);
            //-------------------------
            pivot = left;
            right--;
        }else{
            left++;
        }
    }
}
quickSort(list, 0, right -1);
quickSort(list, right + 1, temp);

As the number of elements I'm sorting gets closer to about 50 the time it takes to sort get exponentially larger. I'm out of ideas. Anyone ever dealt with this before?

edited May 06 '14 at 19:34

Zong

6,160
5
32
46

asked May 06 '14 at 19:32

Donovan King

whats the prototype for quickSort? – Michael May 06 '14 at 19:35
`std::swap` doesn't take 3 arguments. – Alan Stokes May 06 '14 at 20:11
@Ken That's correct behaviour iff the element that ends up at `right` is the pivot. – Alan Stokes May 06 '14 at 20:51
Sure that it is exponential or only quadratic? Try other seeds. Next, I would try replacing std::swap by a plain-old manual swap. – davidhigh May 06 '14 at 21:18

Quicksort won't sort more than 50 elements

0 Answers0