Java implementation of Dijkstra algorithm

Tag: Shortest path Dijkstar greedy algorithm Java

Learn Dijstar algorithm starting from Shortest path

The following is a description of the shortest path problem:

The following is a description of the Dijkstar algorithm:

Here's how to solve the problem in the right graph using the Dijkstar algorithm:

Here is the adjacency matrix of the graph:

Here is the calculation process:

Here's how to solve the shortest path:

Here is the Java code implementation, which need to pay attention to the problem I have marked (must be careful!!!!!) ）:

Package Greedy_algorithm;import Java.util.arraylist;import Java.util.hashmap;import java.util.hashset;import Java.util.map;import Java.util.set;public class Dijkstra {private set<integer> permanent=new hashset<> (); Private set<integer> temporary=new hashset<> ();p rivate map<integer, integer> nodeMap=new HashMap <integer, integer> (); key= permanent node, value= shortest path before a node, improves backtracking efficiency private int [] [] m;private Mark [] d;private int n;private final static int max=65535;c Lass mark{private int Length=max;private int Previous=-1;private boolean ismarked=false;public mark () {}public mark (int Length,int Previous,boolean ismarked) {this.length=length;this.previous=previous;this.ismarked=ismarked;}} Public Dijkstra () {n=6;m=new int[][]{{0, 1, 4,-1,-1,-1}, {1, 0, 2, 7, 5,-1}, {4, 2, 0,-1, 1,-1}, {-1, 7,- 1, 0, 3, 2}, {-1, 5, 1, 3, 0, 6}, { -1,-1,-1, 2, 6, 0}};d =new mark[n][n];for (int i=0;i<n;i++) {for (int j=0;j&lt ; n;j++) {d[i][j]=new Mark ();//system.out.prIntln (d[i][j].length+ "" +d[i][j].previous+ "" +d[i][j].ismarked);}}} Public Dijkstra (int n,int [][]m,mark [][]d) {this.n=n;this.m=m;this.d=d;if (n!=m.length && n!=m[0].length & & N!=d.length && n!=d[0].length) {System.out.println ("Incorrect input format"); System.exit (1);}} public void Shortestpath () {arraylist<mark> vlist;permanent.add (0), for (int i=1;i<n;i++) {temporary.add (i);} D[0][0]=new Mark (0,-1,true), Nodemap.put (0,-1),/*for (int q=0;q<n;q++) System.out.print ("(" +d[0][q].length+ "," +d [0] [q].previous+ "," +d[0][q].ismarked+ "); System.out.println (); */for (int i=1;i<n;i++) {for (int t:temporary) {vlist=new arraylist<dijkstra.mark> (); for (int p:permanent) {if (m[t][p]!=-1) {Vlist.add (New Mark (GetLength (t, p), P,false));}} if (Vlist.size ()!=0) {d[i][t]=getmin (vList);}} Marknode (i);/*for (int r=0;r<n;r++) System.out.print ("(" +d[i][r].length+ "," +d[i][r].previous+ "," +d[i][r "). Ismarked+ ")"); System.out.println (); */}}public void traceBack (int end) {int node=end;for (int i=0;i<n;i+ +) {if (d[i][node].ismarked==true) {System.out.println ("the shortest lenth from V0 to V" +node+ "is:" +d[i][node].length) ;}} System.out.println ("The Shortest Path is:"); Trace (end);} public void trace (int end) {int node =end;if (node>=0) {Trace (Nodemap.get (node)), if (node==5) System.out.print ("V" + node); ElseSystem.out.print ("V" +node+ ");}} public int getlength (int t,int p) {int length=m[t][p];for (int i=0;i<n;i++) {if (d[i][p].ismarked==true) {Length+=d[i] [P].length;break;}} return length;}            Public Mark getmin (arraylist<mark> vList) {Mark mark=new mark (); int Min=max; Notice here must be Min=max, this place of problem looked for a long time of mistake!!! System.out.println ("min=" +min); for (Mark c:vlist) {//system.out.println ("+c.length+", "+c.previous+", "+ C.ismarked+ ")"), if (min>c.length) {min=c.length;mark=c;//system.out.println ("break");}} System.out.println ("+mark.length+", "+mark.previous+", "+mark.ismarked+"); return mark==null?new mark ( -1,-1, false): Mark; public void Marknode (int row) {int min=max;int position=-1;for (int j=0;j<n;j++) {if (D[row][j].length!=max) {if (min>d[row][j].length) {min=d[row][j].length;position=j;}}} if (position!=-1) {d[row][position].ismarked=true;permanent.add (position); Temporary.remove (position); nodemap.put (position, d[row][position].previous);}} public static void Main (string[] args) {Dijkstra dijkstra=new Dijkstra ();d Ijkstra.shortestpath ();/*for (map.entry< Integer, integer> Entry:dijkstra.nodeMap.entrySet ()) System.out.println (entry); */dijkstra.traceback (5);}}

Java implementation of Dijkstra algorithm