經典圖演算法Java代碼實踐：BFS,DFS以及幾種最短路徑演算法

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public class City {String name; int id;static int idCounter = 0;public City(String name) {this.name=name;id = idCounter++;}}

import java.util.ArrayList;public class Graph {public static void main(String[] args){// TODO Auto-generated method stubMap M = new Map(12);City a = new City("a");City b = new City("b");City c = new City("c");City d = new City("d");City e = new City("e");City f = new City("f");City g = new City("g");City h = new City("h");City i = new City("i");City j = new City("j");City k = new City("k");City l = new City("l");M.createEdge(a,b,3);M.createEdge(a,c,5);M.createEdge(a,d,4);M.createEdge(b,f,6);M.createEdge(c,d,2);M.createEdge(c,g,4);M.createEdge(d,e,1);M.createEdge(d,h,5);M.createEdge(e,f,2);M.createEdge(e,i,4);M.createEdge(f,j,5);M.createEdge(g,h,3);M.createEdge(g,k,6);M.createEdge(h,i,6);M.createEdge(h,k,7);M.createEdge(i,j,3);M.createEdge(i,l,5);M.createEdge(j,l,9);M.createEdge(k,l,8);System.out.println("the graph is:\n");System.out.println(M);System.out.println();System.out.println("findPathByDFS:a to k");M.findPathByDFS(a,k);System.out.println();System.out.println("findPathByBFS:a to k");M.findPathByBFS(a,k);System.out.println();System.out.println("bellmanFord from a:");M.bellmanFord(a);System.out.println();System.out.println("dijkstra from a:");M.dijkstra(a);System.out.println();System.out.println("bellmanFord,print example from a:");M.floydWarshall();M.printFloydWarshallForOneCity(a);}}

import java.util.ArrayList;import java.util.LinkedList;import java.util.Queue;public class Map {double[][] A;public Map(int n){A = new double[n][n];     for(int i = 0;i < A.length;i++)     {           for(int j = 0;j < A.length;j++)           {           if(i == j) A[i][j] = 0;           else A[i][j] = -1;           }     }}ArrayList<City> cities = new ArrayList<City>();private double[] D;private void relax(int u,int v){        if(D[v]>D[u]+A[v][u])          D[v]=D[u]+A[v][u];}private double[][] DD = null;public void floydWarshall(){ DD = new double[A.length][A.length];     int i,j,k;     for(i = 0;i < A.length;i++)     {           for(j = 0;j < A.length;j++)           {           if(A[i][j]>0)                 DD[i][j] = A[i][j];           else if(i == j)  DD[i][j] = 0;           else DD[i][j] = 99999999;           }     }     for(k = 0;k < A.length;k++)     for(i = 0;i < A.length;i++)     for(j = 0;j < A.length;j++)     {      if(DD[i][j] > DD[i][k] + DD[k][j])      {          DD[i][j] = DD[i][k] + DD[k][j];       }     }}public void printFloydWarshallForOneCity(City city){System.out.println("floydWarshall:");if(DD == null){floydWarshall();}for(int i=0;i<A.length;i++){System.out.printf("from %s to %s shortest path is:%f\n",city.name,cities.get(i).name,DD[city.id][i]);}}public void dijkstra(City city){dijkstra(city.id);System.out.println("dijkstra:");for(int i=0;i<A.length;i++){System.out.printf("from %s to %s shortest path is:%f\n", city.name,cities.get(i).name,D[i]);}}public void dijkstra(int  srcId){D = new double[A.length];        for(int i=0;i<A.length;i++)       {        D[i]=999999999;            }        D[srcId]=0;        int[] q = new int[A.length];        int ql=0,qf=0; //隊列                for(int i=0;i<A.length;i++) q[ql++]=i;        while(qf!=ql)        {               int min=qf;               for(int i=qf;i<ql;i++)                {               if(D[q[i]]<D[q[min]])                {               min=i;               }               }                        int id = q[qf];               q[qf] = q[min];               q[min] = id; //q[qf] is the min               int u=q[qf++];               for(int i=0;i<A.length;i++)               {                  if(A[u][i]>0)                   {                  relax(u,i);                  }               }        }}public void bellmanFord(City city){bellmanFord(city.id);System.out.println("bellmanFord:");for(int i=0;i<A.length;i++){System.out.printf("from %s to %s shortest path is:%f\n", city.name,cities.get(i).name,D[i]);}}public void bellmanFord(int srcId){D = new double[A.length];for(int i=0;i<A.length;i++){D[i] = 99999999;//無窮大}D[srcId] = 0;for(int i=0;i<A.length;i++)//外層迴圈次數{for(int j=0;j<A.length;j++){for(int k=0;k<A.length;k++){if(A[j][k]>0){relax(j,k);}}}}}Queue<Integer> bfsQueue = new LinkedList<Integer>();boolean[] bfsFlag;int bsfPre[];public void findPathByBFS(City src,City dst){System.out.printf("bfs find path between ‘%s‘ and ‘%s‘!\n",src.name,dst.name);findPathByBFS( src.id, dst.id);printBFS(dst.id);}public void findPathByBFS(int srcId,int dstId){bsfPre = new int[A.length];bfsQueue.clear();bfsFlag = new boolean[A.length];for(int i=0;i<A.length;i++){bfsFlag[i] = false;bsfPre[i] = -1;}bfsQueue.offer(srcId);bfsFlag[srcId] = true;while(!bfsQueue.isEmpty()){int current = bfsQueue.poll();for(int index=0;index<A.length;index++){if(current == index) continue;if(A[current][index]>0) //兩者相連{if(index == dstId)//找到目標了{bfsFlag[index] = true;bsfPre[index] = current;return;//直接返回}if(bfsFlag[index] == false)//假設未訪問過{bfsFlag[index] = true;bsfPre[index] = current;bfsQueue.offer(index);}}}}}private void printBFS(int dstId){int index = dstId;do{System.out.printf("<-%s", cities.get(index).name);index = bsfPre[index];}while(index != -1);System.out.println();}ArrayList<Integer> dfsPath = new ArrayList<Integer>();boolean[] dfsFlag;private void printDFS(){for(Integer node:dfsPath){System.out.printf("->%s", cities.get(node).name);}System.out.println();}public void findPathByDFS(City src,City dst){System.out.printf("dfs find path between ‘%s‘ and ‘%s‘!\n",src.name,dst.name);findPathByDFS(src.id, dst.id);}public void findPathByDFS(int srcId,int dstId){dfsPath.clear();dfsFlag = new boolean[A.length];for(int i=0;i<A.length;i++){dfsFlag[i] = false;}dfsPath.add(srcId);dfsFlag[srcId] = true;dfs( srcId, dstId);printDFS();}private void dfs(int srcId,int dstId){for(int index=0;index<A[srcId].length;index++){if(srcId == index) continue;if(A[srcId][index]>0)//兩者串連{if(index == dstId)//找到目標了{dfsFlag[index] = true;dfsPath.add(index);return;}if(dfsFlag[index] == false)//假設該節點未訪問過{dfsFlag[index] = true;dfsPath.add(index);dfs(index,dstId);if(dfsFlag[dstId] == false)//目標沒找到dfsPath.remove(index);else return;}}}}public void createEdge(City a, City b, double w) {A[a.id][b.id]=w;A[b.id][a.id]=w;//added by me!cities.add(a.id,a);cities.add(b.id,b);}public String toString(){String r = "I am a map of " + A.length + " cities."; r += " My connections are:\n";for (int i=0;i<A.length;i++) {for (int j=0;j<A[0].length;j++)r+=A[i][j]+"\t";r+="\n";}return r;}}

經典圖演算法Java代碼實踐：BFS,DFS以及幾種最短路徑演算法