Dijkestra

vector <pii> g[mx];
priority_queue <pii, vector <pii>, greater <pii> > q;
int dis[mx];

int dijkestra(int a, int b, int n){
    for(int i=1;i<=n;i++) dis[i] = inf;
    dis[a] = 0;
    q.push({0, a});
    while(!q.empty()){
        pii p = q.top();
        q.pop();
        if(dis[p.se]==p.fi){
            for(auto u: g[p.se]){
                if(dis[u.fi] > dis[p.se] + u.se){
                    dis[u.fi] = dis[p.se] + u.se;
                    q.push({dis[u.fi], u.fi});
                }
            }
        }
    }
    return dis[b];
}