Java Related

Primitives vs. References

1. primitive types are the basic types of data

• byte, short, int, long, float, double, boolean, char
• primitive variables store primitive values

2. reference types are any instantiable class as well as arrays

• String, Scanner, Random, Die, int[], String[], etc.
• reference variables store addresses

PriorityQueue in Java

based on the priority heap, First-In-First-Out algorithm, lowest to highest

• PriorityQueue doesn’t permit NULL pointers.
• We can’t create PriorityQueue of Objects that are non-comparable
• PriorityQueue are unbound queues.
• The head of this queue is the least element with respect to the specified ordering. If multiple elements are tied for least value, the head is one of those elements — ties are broken arbitrarily.
• The queue retrieval operations poll, remove, peek, and element access the element at the head of the queue.
• It inherits methods from AbstractQueue, AbstractCollection, Collection and Object class.

PriorityQueue<ListNode> queue = new PriorityQueue<ListNode>(lists.length, (a, b) -> a.val - b.val);

or

PriorityQueue<ListNode> queue= new PriorityQueue<ListNode>(lists.size(),new Comparator<ListNode>(){
    @Override
    public int compare(ListNode o1,ListNode o2){
        if (o1.val<o2.val)
           return -1;
        else if (o1.val==o2.val)
           return 0;
        else 
           return 1;
        }
   });