重载运算符时priority_queue的顺序？

Question

Hi I am trying to understand how the comparator works for priority_queue in c++. It confuses me for a long time.

Let's say we have this struct:

struct compare{
  public:
  bool operator()(Node& a,Node& b) // overloading both operators 
  {
      return a.w < b.w: // if you want increasing order;(i.e increasing for minPQ)
      return a.w > b.w // if you want reverse of default order;(i.e decreasing for minPQ)
   }
};

And we can create the pq in this way:

priority_queue<Node,vector<Node>,compare> pq;

I want to know why "operator<" is minq, ie pq.top() is the minimum? while "operator>" is maxq?

Answer 1

If the ordering function returns true, then the first object will come before the second object.

So if you have

return a.w < b.w;

and it's true then a will come before b .

Same with

return a.w > b.w;

If it's true then a will come before b .

This is well documented .