Dijkstra for MapReduce (1)

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准备研究一下Dijkstra最短路径算法Hadoop上用MapReduce实现的过程。首先温习一下普通Dijkstra算法。

1） 数据结构准备：Graph，包括顶点类Vex，优先队列PQ：

package com.wlu.graph;import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class Graph {private Map<Vex, Map<Vex, Integer>> Vlist;public Graph(Map<Vex, Map<Vex, Integer>> vvv) {Vlist = vvv;}public static Graph CreateFromFile(String fileName) throws IOException {BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(fileName)));Map<Vex, Map<Vex, Integer>> _Vlist = new HashMap<Vex, Map<Vex, Integer>>();Map<String, Vex> name2Vex = new HashMap<String, Vex>();for (String line = br.readLine(); line != null; line = br.readLine()) {String[] vs = line.split(" ");// 3 parts in the lineString vsrc = vs[0];String vdes = vs[1];int wsd = Integer.parseInt(vs[2]);// add to the look up tableVex src = null;Vex dest = null;if (name2Vex.containsKey(vsrc)) {src = name2Vex.get(vsrc);} else {src = new Vex(vsrc);name2Vex.put(vsrc, src);}if (name2Vex.containsKey(vdes)) {dest = name2Vex.get(vdes);} else {dest = new Vex(vdes);name2Vex.put(vdes, dest);}// add the new dest node information// System.err.println(src.getName() + "  " + dest.getName() + "  " +// wsd);if (_Vlist.get(src) == null) {HashMap<Vex, Integer> DestMap = new HashMap<Vex, Integer>();DestMap.put(dest, wsd);_Vlist.put(src, DestMap);} else {_Vlist.get(src).put(dest, wsd);}}br.close();return new Graph(_Vlist);}public String toString() {String s = "";for (Vex src : Vlist.keySet()) {s += src.getName() + ": {";for (Vex des : Vlist.get(src).keySet()) {s += des.getName() + " (" + getw(src, des) + ")} {";}s = s.substring(0, s.length() - 1) + "\n";}return s;}public int getw(Vex u, Vex v) {return Vlist.get(u).get(v);}public int getVexNum() {return Vlist.keySet().size();}public Set<Vex> getVexs() {return Vlist.keySet();}// get AdjacencyList of Vex upublic Map<Vex, Integer> AdjacencyList(Vex u) {return Vlist.get(u);}public static void main(String args[]) throws IOException {Graph g = Graph.CreateFromFile("C:/tmp/test.txt");System.out.print(g.getVexNum() + "\n" + g);}}

package com.wlu.graph;public class Vex {private String name;private int value;public Vex(String n, int v) {name = n;value = v;}public Vex(String n) {name = n;value = 0;}@Overridepublic int hashCode(){return name.hashCode();}@Overridepublic boolean equals(Object v){return name.compareTo(((Vex)v).name) == 0;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getValue() {return value;}public void setValue(int value) {this.value = value;}}

 

package com.wlu.graph;import java.util.ArrayList;
import java.util.List;public class PQ {List<Vex> vlist = new ArrayList<Vex>();public void add(Vex v) {// remove the Vex if has exitfor(int i = 0; i < vlist.size(); i++){if(vlist.get(i).getName().compareTo(v.getName()) == 0){vlist.remove(i);break;}}int i = 0;for (; i < vlist.size(); i++) {if (v.getValue() < vlist.get(i).getValue()) {break;}}// insert v to ith positionList<Vex> vlist2 = new ArrayList<Vex>();int j = 0;for (; j < i; j++) {vlist2.add(vlist.get(j));}vlist2.add(v);for (int k = i; k < vlist.size(); k++) {vlist2.add(vlist.get(k));}vlist = vlist2;}public Vex pop() {if (vlist.size() == 0) {return null;}Vex v = vlist.get(0);vlist.remove(0);return v;}public boolean empty() {return vlist.size() == 0;}public void printPQ() {for (Vex v : vlist) {System.out.print(v.getName() + " (" + v.getValue() + ") ");}System.out.println();}public static void main(String args[]) {PQ pq = new PQ();pq.add(new Vex("a", 12));pq.add(new Vex("b", 2));pq.add(new Vex("c", 1));pq.add(new Vex("d", 123));pq.add(new Vex("e", 33));pq.add(new Vex("f", 4));pq.add(new Vex("g", 0));pq.add(new Vex("h", 21));pq.add(new Vex("i", 5));pq.add(new Vex("j", 3));pq.printPQ();System.out.println(pq.pop().getName());pq.printPQ();}}

 2） Dijkstra算法

package com.wlu.dijkstra;import java.io.IOException;
import java.util.HashMap;
import java.util.Map;import com.wlu.graph.Graph;
import com.wlu.graph.PQ;
import com.wlu.graph.Vex;public class DijkstraSeq {public Graph MST(Graph G, Vex s) {Map<Vex, Integer> d = new HashMap<Vex, Integer>();d.put(s, 0);PQ pq = new PQ();pq.add(s);for (Vex v : G.getVexs()) {if (!v.equals(s)) {d.put(v, Integer.MAX_VALUE);}}while(!pq.empty()){Vex u = pq.pop(); // ExtractMinfor(Vex v : G.AdjacencyList(u).keySet()){if(d.get(v) > d.get(u) + G.getw(u, v)){d.put(v, d.get(u) + G.getw(u, v));v.setValue(d.get(u) + G.getw(u, v));pq.add(v);}}}for(Vex vv : d.keySet()){System.out.println(vv.getName() + "  " + vv.getValue());}return null;}public static void main(String args[]) throws IOException{Graph g = Graph.CreateFromFile("C:/tmp/test.txt");DijkstraSeq dijk = new DijkstraSeq();dijk.MST(g, new Vex("1"));}}