c++ stl correct parameters to priority_queue

Question

Below is the code snippet which is incorrect.

I want to implement dijkstra using priority queue stl of c++. But i cant figure out the right syntax for using this priority_queue with edge class. I want to put edge to priority_queue with based on weights.

class edge{
public: 
    int src;
    int dest;
    int wt;
};

class comp {
bool operator() (int a, int b) {
    if(a<=b){
        return true;
    }else{
        return false;
    }
   }
};


priority_queue<int,edge,comp> check;

edge e1,e2,e3;
e1.dest=1;
e2.dest=2;
e3.dest=3;

Answer 1

#include <queue>
#include <iostream>

class edge{
public:
    int src;
    int dest;
    int wt;
};

struct less_weight {
    bool operator() (const edge& a, const edge& b) {
        return a.wt < b.wt;
    }
};

struct greater_weight {
    bool operator() (const edge& a, const edge& b) {
        return a.wt > b.wt;
    }
};

int main()
{
    std::priority_queue<int,std::vector<edge>,less_weight> prioritise_higher_weights;
    prioritise_higher_weights.push(edge{0, 1, 1 });
    prioritise_higher_weights.push(edge{1, 2, 2 });
    prioritise_higher_weights.push(edge{2, 3, 3 });

    std::priority_queue<int,std::vector<edge>,greater_weight> prioritise_lower_weights;
    prioritise_lower_weights.push(edge{0, 1, 1 });
    prioritise_lower_weights.push(edge{1, 2, 2 });
    prioritise_lower_weights.push(edge{2, 3, 3 });

    std::cout << prioritise_higher_weights.top().wt << std::endl;
    std::cout << prioritise_lower_weights.top().wt << std::endl;
}

expected output:

3
1

Note how priority queue orders by the inverse of the given predicate.