显示错误的Java算法实现

Question

我试图为Dijkstra算法(最短路径树)实现java。图形节点是从一个文本文件中读取的，文本文件包含在顶点之间的字符串(顶点)和int (权重)。但是当运行程序时，它会抛出一个错误。

Exception in thread "main" java.util.InputMismatchException

>at java.util.Scanner.throwFor(Unknown Source)

>at java.util.Scanner.next(Unknown Source)

>at java.util.Scanner.nextInt(Unknown Source)

>at java.util.Scanner.nextInt(Unknown Source)

>at ASD4_dijkstra.main(ASD4_dijkstra.java:94)

这是java的代码

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;



public class ASD4_dijkstra {



    // A utility function to find the vertex with minimum distance value,

    // from the set of vertices not yet included in shortest path tree

    static final int V = 5;

    int minDistance(int dist[], Boolean sptSet[]) {

        // Initialize min value

        int min = Integer.MAX_VALUE, min_index = -1;



        for (int v = 0; v < V; v++)

            if (sptSet[v] == false && dist[v] <= min) {

                min = dist[v];

                min_index = v;

            }



        return min_index;

    }



    // A utility function to print the constructed distance array

    void printSolution(int dist[], int n) {

        System.out.println("Distance from starting vertex");

        for (int i = 0; i < V; i++)

            System.out.println(i + " \t\t " + dist[i]);

    }



    // Funtion that implements Dijkstra's single source shortest path

    // algorithm for a graph represented using adjacency matrix

    // representation

    void dijkstra(int graph[][], int src) {

        int dist[] = new int[V]; // The output array. dist[i] will hold

        // the shortest distance from src to i



        // sptSet[i] will true if vertex i is included in shortest

        // path tree or shortest distance from src to i is finalized

        Boolean sptSet[] = new Boolean[V];



        // Initialize all distances as INFINITE and stpSet[] as false

        for (int i = 0; i < V; i++) {

            dist[i] = Integer.MAX_VALUE;

            sptSet[i] = false;

        }



        // Distance of source vertex from itself is always 0

        dist[src] = 0;



        // Find shortest path for all vertices

        for (int count = 0; count < V - 1; count++) {

            // Pick the minimum distance vertex from the set of vertices

            // not yet processed. u is always equal to src in first

            // iteration.

            int u = minDistance(dist, sptSet);



            // Mark the picked vertex as processed

            sptSet[u] = true;



            // Update dist value of the adjacent vertices of the

            // picked vertex.

            for (int v = 0; v < V; v++)



                // Update dist[v] only if is not in sptSet, there is an

                // edge from u to v, and total weight of path from src to

                // v through u is smaller than current value of dist[v]

                if (!sptSet[v] && graph[u][v] != 0 &&

                    dist[u] != Integer.MAX_VALUE &&

                    dist[u] + graph[u][v] < dist[v])

                    dist[v] = dist[u] + graph[u][v];

        }



        // print the constructed distance array

        printSolution(dist, V);

    }



    // Driver method

    public static void main(String[] args) {

        File file = new File("C:\\Users\\leotr\\Downloads\\alg4.txt");

        try {



            Scanner sc = new Scanner(file);

            int graph[][] = new int[5][5];

            for (int i = 0; i < 5; i++) {

                for (int j = 0; j < 5; j++) {

                    graph[i][j] = sc.nextInt();

                }

            }

            sc.close();

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        }

    }



}

我在谷歌搜索，发现了错误的原因。这是因为文本文件包含int和string，并且在代码中它声明的仅获得int，但无法理解如何更改代码，以使其工作。

编辑：

文本文件

    5// number of nodes into graph

    A,B-6,C-1//name of node and connection with other nodes , and her weight

    B,A-6,C-3,D-7,E-2

    C,A-1,B-3,D-1

    D,B-7,C-1,E-2

    E,B-2,D-2 

文件的第一行是指图中的节点数，其他行表示节点的名称、与其他节点的连接以及连接权重。

例如，A，B-12，C-5表示A与B连接，该连接的权重为12，节点a连接到节点c，权重为5。

我的问题是如何更改循环(主空)，使程序工作(读取文本文件，并计算最短路径树)。

Answer 1

对输入使用nextInt()，它不仅包含整数，还包含逗号和字母等其他字符。你需要把整数和文本分开。

我这样做的方法是使用String.charAt()；

你需要确定每个数字从哪里开始。例如，假设每个节点只能被称为一个1字符长的名称，那么您知道在第5、9、13和17位置有一个整数，特别是您要查找的整数(因为破折号表示为负数)。

因此，要将这些特定整数提取为字符，可以使用String.charAt()并插入数字的索引，这些索引是4的倍数(因为字符串中的位置是4+1的倍数，字符串从索引0开始)。

要获取整数本身，您可以使用String.valueOf()或Integer.parseInt()，在这里您只需插入索引处的字符。

总之，我要这样做的方式如下：

    int nodes = Integer.parseInt(sc.nextLine()); //This takes the first line, the number of nodes and converts it to an integer.
    for(int i = 0; i < nodes; i++){ //This loop will go through each line

        String line = sc.nextLine(); //This extracts each individual line into a string

        for(int j = 4; j < line.length; i+=4){ 
            //This goes through each individual line, through the indexes that are multiples of 4, which we established are the integers you're looking for above.

            String.valueOf(line.charAt(j)); //This returns each integer inside each line in the input text file.

            Integer.parseInt(line.charAt(j)); //This line does the same thing as above.
            /*I'm not sure how to implement this into your algorithm, but I've done the integer extracting bit. 
             * Either of the two lines of code above will give you the integers you're looking for.
            */
        }

    }

要明确的是，我给你的代码只提取了你想要的整数，它实际上并没有把它们放在你需要它们的地方。希望这能帮上忙。