HackerRank - "Breadth First Search: Shortest Reach"

Typical Dijstra algorithm impl. one.

#include <cmath>
#include <cstdio>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
#include <queue>
#include <unordered_map>
#include <unordered_set>
using namespace std;

const long DIST_MAX = -1;

vector<long> dist;
struct Comp
{
    int operator() (const int &v1, const int &v2)
    {
        return dist[v1] > dist[v2];
    }
};
int main() 
{
    int t; cin >> t;
    while (t--)
    {
        unordered_map<int, unordered_set<int>> g;

        int n, m; cin >> n >> m;
        int mm = m;
        while (mm--){
            int x, y;
            cin >> x >> y;
            g[x - 1].insert(y - 1);
            g[y - 1].insert(x - 1);
        }
        int s; cin >> s; s--;
        
        //
        dist.assign(n, DIST_MAX);
        dist[s] = 0;

        // inx
        priority_queue<int, vector<int>, Comp> hp;
        hp.push(s);
        while (!hp.empty())
        {
            int i = hp.top(); hp.pop();

            //    for each children            
            for (auto &c : g[i])
            {
                if (dist[c] == DIST_MAX || (dist[i] + 1) < dist[c])
                {
                    dist[c] = dist[i] + 1;
                    hp.push(c);
                }
            }
        }

        //    output
        for (int i = 0; i < n; i++)
            if (i != s)
            {
                cout << (dist[i] == -1 ? -1 : dist[i] * 6) << " ";
            }
        cout << endl;
    }
    return 0;
}