Aizu Online Judge 1162 Discrete Speed

■1162 Discrete Speed

拡張ダイクストラ．

import java.util.*;
import java.lang.*;
import java.math.*;
import java.io.*;

import static java.lang.Math.*;
import static java.util.Arrays.*;

// AC
public class Main{

 Scanner sc=new Scanner(System.in);

 int INF=1<<28;
 double EPS=1e-9;

 int n, m;
 int s, g;
 LinkedList<E>[] es;

 @SuppressWarnings("unchecked")
 void run(){
  for(;;){
   n=sc.nextInt();
   m=sc.nextInt();
   if((n|m)==0){
    break;
   }
   es=new LinkedList[n];
   for(int i=0; i<n; i++){
    es[i]=new LinkedList<E>();
   }
   s=sc.nextInt()-1;
   g=sc.nextInt()-1;
   for(int i=0; i<m; i++){
    int x=sc.nextInt()-1;
    int y=sc.nextInt()-1;
    int d=sc.nextInt();
    int c=sc.nextInt();
    es[x].add(new E(y, d, c));
    es[y].add(new E(x, d, c));
   }
   solve();
  }
 }

 void solve(){
  // [前][今][前から今の速度]
  double[][][] d=new double[n][n][40];
  PriorityQueue<P> que=new PriorityQueue<P>();
  for(int j=0; j<n; j++){
   for(int i=0; i<n; i++){
    fill(d[j][i], INF);
   }
  }
  d[s][s][1]=0;
  que.offer(new P(s, s, 0, 0));
  for(; !que.isEmpty();){
   P p=que.poll();
   if(d[p.q][p.p][p.v]+EPS<p.d){
    continue;
   }
   for(E e : es[p.p]){
    if(p.q==e.to){
     continue;
    }
    for(int i=-1; i<=1; i++){
     if(p.v+i<=0||p.v+i>e.c){
      continue;
     }
     if(d[p.p][e.to][p.v+i]>p.d+(double)e.d/(p.v+i)+EPS){
      d[p.p][e.to][p.v+i]=p.d+(double)e.d/(p.v+i);
      que.offer(new P(p.p, e.to, p.v+i, d[p.p][e.to][p.v+i]));
     }
    }
   }
  }
  double min=INF;
  for(int i=0; i<n; i++){
   min=min(min, d[i][g][1]);
  }
  println(""+(min<INF/2?min:"unreachable"));
 }

 class E{
  int to, d, c;

  E(int to, int d, int c){
   this.to=to;
   this.d=d;
   this.c=c;
  }
 }

 class P implements Comparable<P>{
  int q, p, v;
  double d;

  P(int q, int p, int v, double d){
   this.q=q;
   this.p=p;
   this.v=v;
   this.d=d;
  }

  @Override
  public int compareTo(P p){
   if(d+EPS<p.d){
    return -1;
   }else if(d>p.d+EPS){
    return 1;
   }else{
    return 0;
   }
  }

 }

 void debug(Object... os){
  System.err.println(Arrays.deepToString(os));
 }

 void print(String s){
  System.out.print(s);
 }

 void println(String s){
  System.out.println(s);
 }

 public static void main(String[] args){
  // System.setOut(new PrintStream(new BufferedOutputStream(System.out)));
  new Main().run();
 }
}