Number of swaps and comparisons in Shaker/Cocktail sort -Java

Question

I have looked at how to count swaps and comparisons for bubble sort and modified a shaker sort program to this:

 public void shakerSort(int a[])  // http://www.geeksforgeeks.org/cocktail-sort/
{
    boolean swapped = true;
    comparisons = 0;
    swaps = 0;
    int start = 0;
    int end = a.length;

    while (swapped==true)
    {         
        swapped = false;

        for (int i = start; i < end-1; ++i)
        {
          comparisons++; //count comparisons
          if (a[i] > a[i + 1])
          {
             int temp = a[i];
             a[i] = a[i+1];
             a[i+1] = temp;
             swapped = true;

             swaps++; //count swaps
          }
        }

        if (swapped==false)
        {
            break; 
        }

        swapped = false;

        end = end-1;

        for (int i = end-1; i >=start; i--)
        {
          comparisons++; //count comparisons
            if (a[i] > a[i+1])
            {
                int temp = a[i];
                a[i] = a[i+1];
                a[i+1] = temp;
                swapped = true;
                swaps++; //count swaps
            }
        }

        start = start+1;

    }

}

However, for an array of 100 elements where the number of comparisons should always be 4950 ( n(n-1)/2 ), it gives me a value that changes every time I run the program- and this value is always less than 4950.

Why does it do this, and how can I fix it?

(NOTE: The array is randomized each time the program is run)

Also, is the swap count okay?

Answer 1

Let's take example and understand changes in count:

array[5] = { 2 , 1 , 3 , 4 , 5 }

How many iterations should it take.?

first, shaker sort will check from start and then from last in every iterations. count is 0 at start.

 2 , 1 , 3 , 4 , 5 --> count = 1
 ^   ^
 it will swap 2 and 1
 swap count++

 1 , 2 , 3 , 4 , 5  --> count = 2
             ^   ^
 no swap

the program will again check because the swap = true

 1 , 2 , 3 , 4 , 5 --> count = 3
     ^   ^
  no swap

 1 , 2 , 3 , 4 , 5  --> count = 4
         ^   ^
 no swap

the program will end because now swap = false.

---

Now lets take different array:

array[5] = { 5 , 4 , 3 , 2 , 1 }

for the same, Iterations will be much more that 4 iterations.!

---

Hence, For same size array and different value, number of iterations will be different.!

Note: swap count and iteration count is used perfect in the the program :)