Number of shortest paths

#define ll long long
#define ar array<ll,2>
class Solution {
public:
    const int mod = 1e9+7;
    void add_self(int &a, int b){
        a+=b;
        if(a>=mod) a-=mod;
    }
    int dijkstra( vector<vector<pair<int,int>>>&g,int n){
        priority_queue<ar, vector<ar>, greater<ar>> pq;
        pq.push({0LL,0LL});
        const int inf = 1e16+5;
        vector<ll>dis(n,inf);
        vector<int>num(n,0);
        dis[0]=0;
        num[0]=1LL;
        while(!pq.empty()){
            auto [dist,node] = pq.top();
            pq.pop();
            if(dis[node]!=dist) continue;
            for(auto [d,to]: g[node]){
                if(dis[node]+d<dis[to]){
                    dis[to] = (dis[node]+d);
                    num[to] = (num[node]%mod);
                    pq.push({dis[to],to});
                }
                else if(dis[node]+d==dis[to]){
                    add_self(num[to],num[node]);
                }
            }
        }
        return num[n-1];
    }
    int countPaths(int n, vector<vector<int>>& roads) {
        vector<vector<pair<int,int>>>g(n);
        for(int i=0;i<(int)roads.size();i++){
            int u=roads[i][0],v=roads[i][1],w=roads[i][2];
            g[u].push_back({w,v});
            g[v].push_back({w,u});
        }
        return dijkstra(g,n);
    }
};