Programming

Am not sure why this is needed? The above algorithm is "hare and tortoise algorithm" where one pointer moves faster 2 nodes at a time and the other slower - 1 node at a time. After the loop, it will detect if there is a loop or will meet the NULL condition.

From within the while-loop , we examined for two cases:

1) A perfect circular condition.

2) A perfect linear condition.


Statement-A:
There is still a remaining case for the 'perfect linear condition' needs to be tested for (END != (b->next)->next); which we are doing with the while-loop condition itself, when the value of b becomes b = (b->next)->next) .



Now What could be the exact conditions when the while-loop ends?

Its the following:


Either
1) (b != END) == FALSE

Or,
2) (a != b) == FALSE


Both these conditions needs to be tested to establish what was the exact condition of the loop-termination to decide the two remaining cases of the list.

The test (b != END) == FALSE definitely needs to be tested to satisfy the statement-A above. Hence this is testing for the Linear case of the list.

The other one is the else-part of it in which the test for ((a != b) == FALSE) is being done and this refers to a case when there is a loop inside the linked list and also that the list is not a 'perfect circular list'. This kind of list assumes a sigma-shape.