CRX-Graph(BFS) | Cyclic Node | NQ, DQ | Queue

#1

In BFS course,

Q1
if you reach at 13:12 ( This is 13 min and 12 sec on the course lecture). The Node C is present in queue two times. So why is this node known as ‘Cyclic Node’.

Q2
If you reach at 21:41 ( Instructor uses term NQ and DQ ). What does this mean ??

Q3:
If you reach at 21:41 ( Instructor uses two pairs for Queue )
af(add first),rL(remove last)
al(add last),rf(remove first)

I understand the complexity but i do not understand how we get the above pairs. Queue is FIFO. So it should be af,rf.

#2

Please ignore query ( CRX-Graph(BFS) | Cyclic Node | NQ, DQ | Queue )

#3

Hey @connectrajanjain I am telling you about Q3 that you asked.
Just take into account FIFO property of Queue So there can be two ways to implement a queue one way is obvious to remove first and add last. But the second way is remove last and add first to learn how this can be queue lets take a example :
initially queue is empty now we have to insert for example 1 in the queue so by assumption we called add first now our queue becomes : 1
now add first 2, 3 also.
So our queue will become :
3 2 1 (Notice the order very carefully)
now accoridn to FIFO 1 has to be removed first and since we have assumed the pair(Add first remove last) So we called remove last and as we can see 1 will be removed.So clearly it follows FIFO but now coming to question why we need this. Here comes the concept of Time complexity.
If you’re dealing with LinkedList then Add last and remove first will be done in 0(1) which is very good.
But what if we have implement queue using an ArrayList???add last(O(1)) and remove first will be O(n).But if do remove lastO(1) and add first(O(n)) by doing this we have made our queue dequeue Efficient for any arraylist.

#4

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#5

You are awesome. Each word make sense. Thanks you for such explanation. All doubts clear.