java.lang.NumberFormatException: For Input string "" - When using scanner to read txt file

Question

I have a problem where I need to implement Dijkstra's algorithm for Single Source Shortest Path Problem with Binary Heaps. The running time should be O(ElogV).

Here is the code for reading in from a scanner:

try {
        Scanner sc = new Scanner(new File("../SOME_TEXT_FILE.txt"));
        String line = sc.nextLine();
        String[] ne = line.split(" ");

        nodes = Integer.parseInt(ne[0].split("=")[1]);
        edges = Integer.parseInt(ne[1].split("=")[1]);

        constructGraph(sc);

The issue happens when the constructGraph(sc) method is called.

Here's that method:

    static void constructGraph(Scanner sc) {
    adjList = new ArrayList[nodes];

    for (int i = 0; i < nodes; i++)
        adjList[i] = new ArrayList<>();

    for (int i = 0; i < nodes && sc.hasNext(); i++) {
        String edge;
        String n = sc.nextLine();
        while (sc.hasNext() && !(edge = sc.nextLine()).isEmpty()) {
            String[] e = edge.trim().split(" ");
            int from, to, weight;

            to = Integer.parseInt(e[0]);
            weight = Integer.parseInt(e[1].trim());
            adjList[Integer.parseInt(n)].add(new Edge(to, weight));
            adjList[to].add(new Edge(Integer.parseInt(n), weight));
        }
    }
}

The error tells me that the issue is in the line that says

weight = Integer.parseInt(e[1].trim());

Here is a sample of the input coming from the text file:

n=1000 m=8544
0
    25    244
   108    275
   140    273
   159    313

1
    24    187
    43    182
    65    331
   155    369
   182    222

2
    31    504
    35    403
   176    249
   229     68

Flood2d · Accepted Answer · 2020-04-18 00:52:51Z

1

Because there are multiple spaces between the two numbers you have to split using a different regex

String[] e = edge.trim().split("\\s+");

Splitting "1 2" using split(" ") will produce an array of size 3 with values ["1", "", "2"] where the middle element is the empty string delimited by the left and right space character. Using \\s+ you are saying that you want to split sequences separated by a sequence of whitespace characters.

edited Apr 18, 2020 at 0:52

answered Apr 18, 2020 at 0:47

Flood2d

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