【发布时间】：2014-03-16 17:39:53
【问题描述】：
在不使用 Comparator 接口的情况下在 java 中实现 Dijkstra。
【问题讨论】：
标签： dijkstra
【发布时间】：2014-03-16 17:39:53
【问题描述】：
首先你可以在这里阅读算法伪代码：http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
这里是比较器的一种很好的工作方式。但是您必须创建节点、图形等类。 如果比较器是您的问题，只需创建您自己的！ ;)
static class distance_Comparator implements Comparator<node>
{
public int compare(node x, node y)
{
if(x.getDistance()<y.getDistance())
{
return -1;
}
else if(x.getDistance()>y.getDistance())
{
return 1;
}
return 0;
}
}
这里是 Dijkstra
public static void Dijkstra(graph newgraph)
{
System.out.println("--------------------------------------------------------------------------------------");
System.out.println("--------------------------------------------------------------------------------------");
System.out.println("Running Dijkstra . . . .");
System.out.println("--------------------------------------------------------------------------------------");
System.out.println("--------------------------------------------------------------------------------------");
int sum_average_path=0,average_path=0,numberof_paths=0;
long time_a=System.nanoTime();
//[newgraph.getNum_nodes()]; // shortest known distance from "vertex"
//HashMap visited=new HashMap<>();//[newgraph.getNum_nodes()]; // all false initially
//[newgraph.getNum_nodes()]; // preceeding node in path
distance_Comparator comparator=new distance_Comparator();
PriorityQueue<node> queue = new PriorityQueue<node>((int) newgraph.getNumber_of_nodes(),comparator);
///////// find max shortest path : diameter of graph ////////////////
double diameter=-1.0;
int s=0,i=0;
double alt=0;
HashMap map;
///////////find all nodes of graph/////////////////
map=newgraph.getAll_graph_nodes();
for (Object key : map.keySet())
{
i++;
// System.out.println("source node: "+key);
///////////////////Initializations////////////////////////////
/////////////////////////////////////////////////////////////
HashMap distance=new HashMap<>(16,0.6f);
HashMap previous=new HashMap<>(16,0.6f);
node tmpnode=(node)map.get(key);
for (Object key_other : map.keySet())
{
node x_tmpnode=(node)map.get(key_other);
distance.put(key_other, Double.POSITIVE_INFINITY);
x_tmpnode.setDistance(Double.POSITIVE_INFINITY);
x_tmpnode.setVisited(false);
}
tmpnode.setDistance_table(distance);
tmpnode.setPrevious_table(previous);
/////////////////////////////////////end of init//////////////////////////////
tmpnode.setDistance((double)(0));
queue.offer(tmpnode); //add tmp node to PriorityQueue
distance.put(key,(double)(0));
Stack sta=new Stack();
while(queue.isEmpty()==false)
{
Stack stack_prev=new Stack();
node queue_tmpnode=queue.poll(); //min_node(distance,map);////vertex in Q with smallest distance in dist[] and has not been visited;
queue_tmpnode.setVisited(true);
/* if(queue_tmpnode.getPrevious_table()!=null)
{
// System.out.println("pre: "+prev);
Stack tmp=(Stack)tmpnode.getPrevious_table().get(queue_tmpnode.getName());
while(tmp.empty()==false)
{
sta.add(queue_tmpnode.getName());
//System.out.println("pop: "+tmp.pop().toString());
queue_tmpnode=
}
}*/
HashMap queue_tmpnodemap=(HashMap)queue_tmpnode.getMap();
if(queue_tmpnodemap!=null)
{
//////////////find all Neighbours of node queue_tmpnode////////////////////
for (Object v : queue_tmpnodemap.keySet())
{
// System.out.println(" v: "+ v.toString());
node tmpnode_neighbors=(node)map.get(v);
alt=(double)(queue_tmpnode.getDistance()) ;
edge tmp_edge= (edge) (queue_tmpnodemap.get(v)); // dist_between(u, v); --accumulate shortest dist from source
alt+= tmp_edge.getWeight();
if ( (alt < tmpnode_neighbors.getDistance()))
{
tmpnode_neighbors.setDistance(alt); // keep the shortest dist from src to v
distance.put(v, alt);
/*
stack_prev.add(tmpnode_neighbors.getName());
HashMap pre_map=new HashMap();
pre_map.put(queue_tmpnode.getName(), stack_prev);
previous.put(tmpnode_neighbors.getName(), pre_map);
//System.out.println("prev stack: "+stack_prev.size());
tmpnode.setPrevious_table(previous);
* */
if((tmpnode_neighbors.isVisited()==false))
queue.add(tmpnode_neighbors); // Add unvisited v into the Q to be processed
}
}
}
}
HashMap tmp_d=null;
tmp_d=new HashMap();
for(Object x: distance.keySet())
{
if(Double.parseDouble(distance.get(x).toString()) < Double.POSITIVE_INFINITY && Double.parseDouble(distance.get(x).toString())!=0)
{
//System.out.println("U: "+key+"-> V:"+x+" value: "+t_tmpnode.getDistance_table().get(x));
tmp_d.put(x, distance.get(x));
}
}
// System.out.println("V:"+i+" size:"+tmp_d.size()+" capacity:");
distance.clear();
tmpnode.setDistance_table(tmp_d);
}
System.out.println("---------------Dijkstra algorithm-------------");
for (Object key : map.keySet())
{
node tmpnode=(node)map.get(key);
// System.out.println("distance of: "+key.toString()+" , is: ");
//System.out.print("U: "+key);
if(tmpnode.getDistance_table()!= null)
{
//System.out.println(" dipla monopatia: "+(tmpnode.getShortest_paths_number()-tmpnode.getDistance_table().size()));
for(Object x: tmpnode.getDistance_table().keySet())
{
//if(Double.parseDouble(tmpnode.getDistance_table().get(x).toString()) < Double.POSITIVE_INFINITY && Double.parseDouble(tmpnode.getDistance_table().get(x).toString())!=0)
//System.out.println("U: "+key+"-> V:"+x+" value: "+tmpnode.getDistance_table().get(x));
if(diameter < (double)tmpnode.getDistance_table().get(x))
{
diameter= (double)tmpnode.getDistance_table().get(x);
}
sum_average_path+=(double)tmpnode.getDistance_table().get(x);
numberof_paths++;
}
}
System.out.println("\n--------------------------------------------");
for(Object prev: tmpnode.getPrevious_table().keySet())
{
System.out.print("node: "+tmpnode.getName()+" path: ");
HashMap map_prev=(HashMap)tmpnode.getPrevious_table().get(prev);
for(Object prev_path: map_prev.keySet())
{
System.out.println("V: "+prev+" -> "+prev_path+"");
Stack tmp=(Stack) map_prev.get(prev_path);
System.out.println("stacksize: "+tmp.size());
while(tmp.empty()==false)
{
System.out.println("pop: "+tmp.pop().toString());
}
}
}
}
newgraph.setDiameter(diameter);
System.out.println("Graph diameter is: "+newgraph.getDiameter());
System.out.println("average path lenght: "+((double)((double)sum_average_path/(double)numberof_paths)));
long time_b=System.nanoTime();
System.out.println("Dijkstra time: "+(time_b-time_a)+" time in seconds: "+(double)((time_b-time_a)/1000000000.0));
}
类：node.java
import java.util.HashMap;
public class node {
private int name;
private HashMap map;
private double pagerank_old;
private double pagerank_new;
private double point_to_me;
private HashMap point_to_me_table;
private double point_to_other;
private HashMap betweenness;
private double betweenness_ofvertex;
private int num_nodes;
private double cluster_coefficient;
private int index;
private int lowlink;
private int shortest_paths_number;
private double distance;
private boolean visited;
private int hub_score;
private int auth_score;
private HashMap distance_table;
private HashMap previous_table;
//private edge edge;
public node(int name,HashMap map)
{
this.name=name;
this.map=map;
}
public node(int name)
{
this.name=name;
}
/**
* @return the name
*/
public int getName() {
return name;
}
/**
* @param name the name to set
*/
public void setName(int name) {
this.name = name;
}
/**
* @return the map
*/
public HashMap getMap() {
return map;
}
/**
* @param map the map to set
*/
public void setMap(HashMap map) {
this.map = map;
}
/**
* @return the pagerank_old
*/
public double getPagerank_old() {
return pagerank_old;
}
/**
* @param pagerank_old the pagerank_old to set
*/
public void setPagerank_old(double pagerank_old) {
this.pagerank_old = pagerank_old;
}
/**
* @return the pagerank_new
*/
public double getPagerank_new() {
return pagerank_new;
}
/**
* @param pagerank_new the pagerank_new to set
*/
public void setPagerank_new(double pagerank_new) {
this.pagerank_new = pagerank_new;
}
/**
* @return the pont_to_me
*/
public double getPoint_to_me() {
return point_to_me;
}
/**
* @param pont_to_me the pont_to_me to set
*/
public void setPoint_to_me(double pont_to_me) {
this.point_to_me = pont_to_me;
}
/**
* @return the point_to_other
*/
public double getPoint_to_other() {
return point_to_other;
}
/**
* @param point_to_other the point_to_other to set
*/
public void setPoint_to_other(double point_to_other) {
this.point_to_other = point_to_other;
}
/**
* @return the distance
*/
public double getDistance() {
return distance;
}
/**
* @param distance the distance to set
*/
public void setDistance(double distance) {
this.distance = distance;
}
/**
* @return the visited
*/
public boolean isVisited() {
return visited;
}
/**
* @param visited the visited to set
*/
public void setVisited(boolean visited) {
this.visited = visited;
}
/**
* @return the distance_table
*/
public HashMap getDistance_table() {
return distance_table;
}
/**
* @param distance_table the distance_table to set
*/
public void setDistance_table(HashMap distance_table) {
this.distance_table = distance_table;
}
/**
* @return the previous_table
*/
public HashMap getPrevious_table() {
return previous_table;
}
/**
* @param previous_table the previous_table to set
*/
public void setPrevious_table(HashMap previous_table) {
this.previous_table = previous_table;
}
public int getHub_score()
{
return hub_score;
}
public void setHub_score(int sc)
{
this.hub_score=sc;
}
public int getAuth_score()
{
return auth_score;
}
public void setAuth_score(int sc)
{
this.auth_score=sc;
}
/**
* @return the point_to_me_table
*/
public HashMap getPoint_to_me_table() {
return point_to_me_table;
}
/**
* @param point_to_me_table the point_to_me_table to set
*/
public void setPoint_to_me_table(HashMap point_to_me_table) {
this.point_to_me_table = point_to_me_table;
}
/**
* @return the betweenness
*/
public HashMap getBetweenness() {
return betweenness;
}
/**
* @param betweenness the betweenness to set
*/
public void setBetweenness(HashMap betweenness) {
this.betweenness = betweenness;
}
/**
* @return the cluster_coefficient
*/
public double getCluster_coefficient() {
return cluster_coefficient;
}
/**
* @param cluster_coefficient the cluster_coefficient to set
*/
public void setCluster_coefficient(double cluster_coefficient) {
this.cluster_coefficient = cluster_coefficient;
}
/**
* @return the betweenness_ofvertex
*/
public double getBetweenness_ofvertex() {
return betweenness_ofvertex;
}
/**
* @param betweenness_ofvertex the betweenness_ofvertex to set
*/
public void setBetweenness_ofvertex(double betweenness_ofvertex) {
this.betweenness_ofvertex = betweenness_ofvertex;
}
/**
* @return the shortest_paths_number
*/
public int getShortest_paths_number() {
return shortest_paths_number;
}
/**
* @param shortest_paths_number the shortest_paths_number to set
*/
public void setShortest_paths_number(int shortest_paths_number) {
this.shortest_paths_number = shortest_paths_number;
}
/**
* @return the num_nodes
*/
public int getNum_nodes() {
return num_nodes;
}
/**
* @param num_nodes the num_nodes to set
*/
public void setNum_nodes(int num_nodes) {
this.num_nodes = num_nodes;
}
/**
* @return the index
*/
public int getIndex() {
return index;
}
/**
* @param index the index to set
*/
public void setIndex(int index) {
this.index = index;
}
/**
* @return the lowlink
*/
public int getLowlink() {
return lowlink;
}
/**
* @param lowlink the lowlink to set
*/
public void setLowlink(int lowlink) {
this.lowlink = lowlink;
}
}
类：边缘
public class edge {
private int a;
private int b;
private double weight;
//private double betweenness;
public edge(int start,int end,double weight){
this.a=start;
this.b=end;
this.weight=weight;
}
/**
* @return the a
*/
public int getA() {
return a;
}
/**
* @param a the a to set
*/
public void setA(int a) {
this.a = a;
}
/**
* @return the b
*/
public int getB() {
return b;
}
/**
* @param b the b to set
*/
public void setB(int b) {
this.b = b;
}
/**
* @return the weight
*/
public double getWeight() {
return weight;
}
/**
* @param weight the weight to set
*/
public void setWeight(double weight) {
this.weight = weight;
}
}
类：图形
import java.util.HashMap;
import java.util.Stack;
public class graph {
private HashMap all_graph_nodes;
private double number_of_nodes;
private double number_of_edges;
private double diameter;
private double average_degre;
private double density;
private int nodeindex;
private Stack tarjanStack;
public graph(HashMap map,double n_nodes,double m_edges)
{
this.all_graph_nodes=map;
this.number_of_nodes=n_nodes;
this.number_of_edges=m_edges;
}
/**
* @return the all_graph_nodes
*/
public HashMap getAll_graph_nodes() {
return all_graph_nodes;
}
/**
* @param all_graph_nodes the all_graph_nodes to set
*/
public void setAll_graph_nodes(HashMap all_graph_nodes) {
this.all_graph_nodes = all_graph_nodes;
}
/**
* @return the number_of_nodes
*/
public double getNumber_of_nodes() {
return number_of_nodes;
}
/**
* @param number_of_nodes the number_of_nodes to set
*/
public void setNumber_of_nodes(double number_of_nodes) {
this.number_of_nodes = number_of_nodes;
}
/**
* @return the number_of_edges
*/
public double getNumber_of_edges() {
return number_of_edges;
}
/**
* @param number_of_edges the number_of_edges to set
*/
public void setNumber_of_edges(double number_of_edges) {
this.number_of_edges = number_of_edges;
}
/**
* @return the diameter
*/
public double getDiameter() {
return diameter;
}
/**
* @param diameter the diameter to set
*/
public void setDiameter(double diameter) {
this.diameter = diameter;
}
/**
* @return the average_degre
*/
public double getAverage_degre() {
return average_degre;
}
/**
* @param average_degre the average_degre to set
*/
public void setAverage_degre(double average_degre) {
this.average_degre = average_degre;
}
/**
* @return the density
*/
public double getDensity() {
return density;
}
/**
* @param density the density to set
*/
public void setDensity(double density) {
this.density = density;
}
/**
* @return the nodeindex
*/
public int getNodeindex() {
return nodeindex;
}
/**
* @param nodeindex the nodeindex to set
*/
public void setNodeindex(int nodeindex) {
this.nodeindex = nodeindex;
}
/**
* @return the tarjanStack
*/
public Stack getTarjanStack() {
return tarjanStack;
}
/**
* @param tarjanStack the tarjanStack to set
*/
public void setTarjanStack(Stack tarjanStack) {
this.tarjanStack = tarjanStack;
}
}
【讨论】：