How to sort the map based on value in c++ using stl?

Question

struct node{
    int index;
    int count;
};

map<int,struct node *> m1;

bool compare(struct node* a, struct node* b) {
    if(a->count>b->count)
        return 1;
    if(a->count==b->count && a->index<b->index)
        return 1;
    return 0;
}

Can i sort the map based on greater count value and if count is equal then based on lower index value?

A way is to push all the values in vector and perform sort. Is there any other way by which sorting can be done using priority queue as below?

 priority_queue<pair<int,struct node *>, vector<int,struct node *>, compare> pq(m1.begin(),m1.end());

I have provided the compare function above.

Answer 1

Solution using priority_queue

  class compare {
    public:
        bool operator()(pair<int,struct node *> a, pair<int,struct node *> b)  {
         if(a.second->count>b.second->count)
            return 0;
        if(a.second->count==b.second->count && a.second->index<b.second->index)
            return 0;
        return 1;
        }
    };

   priority_queue<pair<int,struct node *>, vector<pair<int,struct node *> >, compare > pq(m1.begin(),m1.end());