using priority queue in c how to arrange elements in increasing order-CodePudding

typedef vector<vector<int> > board;
typedef pair<board,char> vec; 
priority_queue<pair<int,vec> > q;

how to arrange in asending order depending on the int value?

CodePudding user response：

You should provide the template argument also for the compare function: in other words, you should state how two pairs of <int, vec> should be compared. Check the documentation here At the moment you are using the std:less of pair, it does what stated here

CodePudding user response：

Nothing in what you currently have should stop a basic priority queue of pair<int,vec>. However, that queue will order in descending priority (e.g. highest comes first) by using std::less<T> as the priority determinate.

If you want ascending priority (e.g. lower values are higher-priority), you need to reverse the comparator. I.e. std::greater<T>. An example appears below:

#include <iostream>
#include <random>
#include <vector>
#include <queue>

typedef std::vector<std::vector<int> > board;
typedef std::pair<board,char> vec; 
typedef std::pair<int,vec> elem;
std::priority_queue<elem, std::deque<elem>, std::greater<elem>> q;

int main()
{
    std::mt19937 rng{ std::random_device{}() };
    std::uniform_int_distribution<> dist(1,100);

    // add ten random picks for pair int value
    for (int i=1; i<=10;   i)
        q.push(std::make_pair(dist(rng), vec{}));

    while (!q.empty())
    {
        auto obj = std::move(q.top());
        q.pop();
        std::cout << obj.first << '\n';
    }

}

Output (varies, obviously)