Question

I have been trying to understand this code for hours unsuccessfully. I wrote my own version of bead sort algorithm however it is so slow.
I want to understand why this one works so much more quickly.
Here’s info about the bead sort algorithm:
http://demonstrations.wolfram.com/ExtendedBeadSort/
Can you please help me to understand how this algorithm works?

#include <iostream>
#include <vector>

using std::cout;
using std::vector;

void distribute(int dist, vector<int> &List) {
    //*beads* go down into different buckets using gravity (addition).
    if (dist > List.size() )
        List.resize(dist); //resize if too big for current vector

    for (int i=0; i < dist; i++)
        List[i]++;
}

vector<int> beadSort(int *myints, int n) {
    vector<int> list, list2, fifth (myints, myints + n);
    cout << "sakums\n";
    cout << myints<< "\n";
 //   for (vector<int>::iterator it = fifth.begin(); it != fifth.end(); ++it) cout << " " << *it << "\n";
    cout << "beigas\n";

    cout << "#1 Beads falling down: ";
    for (int i=0; i < fifth.size(); i++)
        distribute (fifth[i], list);
    cout << '\n';

    cout << "\nBeads on their sides: ";
    for (int i=0; i < list.size(); i++)
        cout << " " << list[i];
    cout << '\n';

    //second part

    cout << "#2 Beads right side up: ";
    for (int i=0; i < list.size(); i++)
        distribute (list[i], list2);
    cout << '\n';

    return list2;
}

int main() {
    int myints[] = {734,3,1,24,324,324,32,432,42,3,4,1,1};
    vector<int> sorted = beadSort(myints, sizeof(myints)/sizeof(int));
    cout << "Sorted list/array";
    for(unsigned int i=0; i<sorted.size(); i++)
        cout << sorted[i] << ' ';
    system("PAUSE");
    return 0;
}

Answer 1

Because of how distribute works:

Each of the other numbers contribute “beads” to the slots – there are 13 numbers so slot 1 has 13 in it when it finishes the first pass.

it “distributes” beads in “columns” I.e when you print it on its side, there are now 734 slots – the largest number.

When distribute runs again it shifts the “beads” down by summing the columns – it will perform a number of additions dependent on the max element * The number of numbers – plus memory allocations