CODEWITHSUNDEEP
c++priority-queue
user5965026
user5965026

Reputation: 485

Modifying top of priority queue of custom objects

Suppose that I have a custom struct

struct custom
{
  int quantity;
  double price;
}

and a priority queue of custom objects:

std::priority_queue<custom, std::vector<custom>, some_custom_comparer_t> pq{...}

The some_custom_comparer_t will only sort custom based on price only and not quantity. Is there any way to make it so I can change the quantity of the custom object at the top of the priority queue?

I understand that I won't be able to change the price because the STL container does not allow for adjusting the keys of of the priority queue, but in this case, I want the code to recognize that the quantity variable is not a key and allow me to modify it.

So far, my solution is to pop it off, adjust the quantity, and push it back in.

Upvotes: 0

Views: 678

Answers (1)

Drew Dormann
Drew Dormann

Reputation: 63735

Make the quantity mutable. A mutable member of a class may be modified, even in the context of a const class instance.

struct custom
{
  mutable int quantity;
  double price;
};

So far, my solution is to pop it off, adjust the quantity, and push it back in.

Now you can just do:

sq.top().quantity = new_quantity;

Upvotes: 2

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