Stack + Queue + Priority queue

                                                    STACK

//while pushing top++ and while pop top--

in full stack TOP=Max-1 and empty stack ->top = -1

Stack is full and we are pushing => overflow

Stack is empty and we are popping => underflow

 

                                                QUEUE

empty queue -> front = -1  and rear = -1

if inserted ,i.e., enqueue => rear++

if deleted ,i.e., dequeue => front++

{NOTE:- front is index before first element}

eg.- _523 =>front is 0 bcz 1st element '5' is at index 1

                                            Priority Queue

1. Instead can also use set<>
2. Use max heap to maintain internal order
• priority_queue <int> pq;
3. If want to implement min heap => 
• priority_queue <int, vector<int>, greater<int> > pq;
• here vi stores data values
• NOTE :- this is stored in reverse order means for max heap => max element is last element of vi
• priority_queue <int, vector<int>, cmp > pq;
• for customized comparison
• cmp must be in struct or as class for operator overloading
• Use max heap but multiply all element by -1 at time of use/print => again multiply -1
4. To build heap => O(n)
5. To pop/push => O(log n)
6. priority_queue <int> pq(arr,arr+n);
• Can use to copy existing array