Question

这是一个学校项目;我遇到了很多麻烦，我似乎无法找到一个可以理解的解决方案。

   a b c d e z
 a - 2 3 - - -
 b 2 - - 5 2 -
 c 3 - - - 5 -
 d - 5 - - 1 2
 e - 2 5 1 - 4
 z - - - 2 4 -

这是二维数组。因此，如果你想找到最短的路径，它来自a，b，e，d，z = 7，和（a，b）=（b，a） - 它会带你到行的相邻的新行路径

有没有人可以帮助我为这个例子实现Dijkstra的算法？我真的很感激。（我似乎最喜欢数组，地图和集合让我感到困惑，列表是可管理的 - 虽然我现在愿意考虑任何类型的解决方案）

[至少我不只是从网上扯下来源。我其实想要学习这些东西......这真的很难（＆gt;。＆lt;）]

哦，起点是A，终点是Z

和大多数人一样，我没有发现算法的概念很难 - 我只能看到编码正确...请帮助吗？

示例代码 - 一位朋友帮我解决了这个问题（虽然它充满了我觉得难以理解的数据结构）我还尝试过改编来自dreamincode.net/forums/blog/martyr2/index的C ++代码.php？showentry = 578进入java，但是进展不顺利......

import java.util.*;

public class Pathy{

    private static class pathyNode{
        public final String name;
        public Map<pathyNode, Integer> adjacentNodes;

        public pathyNode(String n){
            name = n;
            adjacentNodes = new HashMap<pathyNode, Integer>();
        }

    }

    //instance variables

    //constructors

    //accessors

    //methods
    public static ArrayList<pathyNode> convert(int[][] inMatrix){
        ArrayList<pathyNode> nodeList = new ArrayList<pathyNode>();
        for(int i = 0; i < inMatrix.length; i++){
            nodeList.add(new pathyNode("" + i));
        }
        for(int i = 0; i < inMatrix.length; i++){
            for(int j = 0; j < inMatrix[i].length; j++){
                if(inMatrix[i][j] != -1){
                    nodeList.get(i).adjacentNodes.put(nodeList.get(j),
                            new Integer(inMatrix[i][j]));
                }
            }
        }
        return nodeList;
    }

    public static Map<pathyNode, Integer> Dijkstra(ArrayList<pathyNode> inGraph){
        Set<pathyNode> visited = new HashSet<pathyNode>();
        visited.add(inGraph.get(0));
        pathyNode source = inGraph.get(0);
        Map answer = new TreeMap<pathyNode, Integer>();
        for(pathyNode node : inGraph){
            dijkstraHelper(visited, 0, source, node);
            answer.put(node, dijkstraHelper(visited, 0, source, node));
        }
        return answer;
    }

    private static int dijkstraHelper(Set<pathyNode> visited, int sum, pathyNode start, pathyNode destination){
        Map<pathyNode, Integer> adjacent = new HashMap<pathyNode, Integer>();

        for(pathyNode n : visited){
            for(pathyNode m: n.adjacentNodes.keySet()){
                if(adjacent.containsKey(m)){
                    Integer temp = n.adjacentNodes.get(m);
                    if(temp < adjacent.get(m)){
                        adjacent.put(m, temp);
                    }
                }
                else{
                    adjacent.put(m, n.adjacentNodes.get(m));
                }
            }
        }

        Map<pathyNode, Integer> adjacent2 = new HashMap<pathyNode, Integer>();
        Set<pathyNode> tempSet = adjacent.keySet();
        tempSet.removeAll(visited);
        for(pathyNode n: tempSet){
            adjacent2.put(n, adjacent.get(n));
        }
        adjacent = adjacent2;
        Integer min = new Integer(java.lang.Integer.MAX_VALUE);
        pathyNode minNode = null;

        for(pathyNode n: adjacent.keySet()){
            Integer temp = adjacent.get(n);
            if(temp < min){
                min = temp;
                minNode = n;
            }
        }
        visited.add(minNode);
        sum += min.intValue();
        sum = dijkstraHelper(visited, sum, start, destination);
        return sum;
    }

    //main
    public static void main(String[] args){

        int[][] input = new int[][] { {-1, 2, 3, -1, -1, -1},
                          {2, -1, -1, 5, 2, -1},
                          {3, -1, -1, -1, 5, -1},
                          {-1, 5, -1, -1, 1, 2},
                          {-1, 2, 5, 1, -1, 4},
                          {-1, -1, -1, 2, 4, -1},
                        };
                        //-1 represents an non-existant path

        System.out.println(Dijkstra(convert(input)));
    }
}

Answer 1

您正在调用2D数组的表示形式是图形的邻接矩阵表示，您尝试解决的问题是“单源最短路径”问题的实例。 Dijkstra的算法旨在解决此类问题。这可能会有所帮助http://renaud.waldura.com/doc/java/dijkstra/。从站点下载代码并阅读文档。基本上你需要编写类似于下面的代码

    RoutesMap map = map =  new DenseRoutesMap(5);
    map.addDirectRoute(City.A, City.B, 2);
    map.addDirectRoute(City.A, City.C, 3);
    map.addDirectRoute(City.B, City.A, 2);
    map.addDirectRoute(City.B, City.D, 5);
    map.addDirectRoute(City.B, City.D, 2);
    ...
    DijkstraEngine engine = new DijkstraEngine(map);
    int distance = engine.getShortestDistance(City.F);

Java中二维数组的Dijkstra算法

2 个答案: