public DijkstraSP(EdgeWeightedDigraph G, int s) {
    distTo = new double[G.V()];                  
    edgeTo = new DirectedEdge[G.V()];            
    for (int v = 0; v < G.V(); v++) {
       distTo[v] = Double.POSITIVE_INFINITY;
    }
    distTo[s] = 0.0;                             
                                                 
    // relax vertices in order of distance from s
    pq = new IndexMinPQ<Double>(G.V());    
    pq.insert(s, distTo[s]);                     
    while (!pq.isEmpty()) {                      
       int v = pq.delMin();                      
       for (DirectedEdge e : G.adj(v))           
          relax(e);                              
       }
    }
}

private void relax(DirectedEdge e) {
  int v = e.from(), w = e.to();
  if (distTo[w] > distTo[v] + e.weight()) {
    distTo[w] = distTo[v] + e.weight();
    edgeTo[w] = e;
    if (pq.contains(w)) {
      pq.change(w, distTo[w]);
    } else {
      pq.insert(w, distTo[w]);
    }
  }
}