java - 在邻接矩阵中运行 Dijkstra 算法后，线程 "main"java.lang.StackOverflowError 中出现异常

Question

我试图在加权邻接矩阵中运行 Dijkstra 算法后打印最短路径。尝试打印路径时出现 stackoverflow 错误。

我已经尝试将起始节点更改为 long 和 BigInteger 类型，正如该平台上之前的答案所建议的那样，我也知道我正在使用递归方法，从而解决了这个问题。

import java.util.*;

public class djikstra {

private static final int invalid = -1;

public djikstra(int matrix[][],int start) {

    int numVertices = matrix[0].length;
    int [] distances = new int [numVertices];
    boolean [] isAdded = new boolean[numVertices];

    for (int i=0;i<numVertices;i++) {
        distances[i]= Integer.MAX_VALUE;
        isAdded[i] = false;
    }

    distances[(int) start]=0;
    int [] parents = new int [numVertices];
    parents[start] = invalid;

    for(int i=1;i<numVertices;i++) {
        int closestNeighbour = -1;
        int shortDist = Integer.MAX_VALUE;

    for(int j=0; j <numVertices;j++) {
        if(!isAdded[j] && distances[j]<shortDist) {
            closestNeighbour = j;
            shortDist = distances[j];
        }
    }
    isAdded[closestNeighbour]=true;

    for(int j = 0; j <numVertices;j++) {
        int edgeDist = matrix[closestNeighbour][j];
        if(edgeDist > 0 && ((closestNeighbour+edgeDist)<distances[j])) {
            parents[j] = closestNeighbour;
            distances[j] = shortDist + edgeDist;
        }
    }
}
    printSol(start,distances,parents);
 }

private static void printSol(int start,int[] distances,int[] parents) {
    int numVertices=distances.length;
    for(int i=0;i<numVertices;i++) {
        if(i !=start) {
            path(i,parents);
        }
 }
}

private static void path(int curr,int[]parents) {
    if(curr== -1) {
        return;
    }

    path(parents[curr],parents);

}
}

public static void Main(String args[]){
       int matrix2[][]= {{0, 0, 0, 4, 12, 14, 0, 0, 0, 0, 0 ,0, 0, 0}, 
           {0, 0, 0, 0, 0, 0, 0, 12, 0, 8, 0, 18, 15, 7},
           {0, 0, 0, 11, 3, 3, 0, 0, 0, 0, 0, 13, 8, 10}, 
           {4, 0, 0, 0, 10, 12, 0, 0, 0, 0, 10, 10, 13, 0}, 
           {0, 0, 3, 10, 0, 2, 0, 0, 0, 0, 0, 10, 5, 11}, 
           {0, 0, 3, 12, 2, 0, 0, 0, 0, 0, 0, 10, 5, 9 },
           {20, 0, 0, 0, 0, 0, 0, 14, 10, 20, 16, 22, 0, 0}, 
           {0, 12, 0, 0, 0 ,0 ,14, 0, 4, 6, 12, 0,0, 0 },
           {0, 16, 0, 0, 0, 0, 10, 4, 0, 10, 14, 20, 0, 0}, 
           {0, 8, 0, 0, 0, 0, 0, 6, 10, 0, 18, 0, 0, 15 },
           {0, 0, 0, 10, 0, 0, 0, 12, 0, 0, 0, 6, 11, 11}, 
           {0, 0, 0, 10, 10, 10, 0, 0, 0, 0, 6, 0, 5, 11}, 
           {0, 0, 8, 0, 5, 5, 0, 0, 0, 0, 11, 5, 0, 8}, 
           {0, 7, 10, 0, 11, 9, 0, 0, 0, 0, 0, 11, 8, 0}};

    djikstra doDjikstra = new djikstra(matrix2,0);
}   



Expected results:
0 4 13 1
Actual results:
Exception in thread "main" java.lang.StackOverflowError
at helperclasses.djikstra.path(djikstra.java:61)

Answer 1

StackOverflowError 是由 path 方法中的无限递归触发的。parents[curr] 永远不会保持 -1(基本情况)，因此递归永远不会停止。您需要确保最终为 curr 调用 path 并使用 -1。