如何将包含矩阵的文件读取为向量的向量？

Posted 2021-05-03

我有一个包含以下格式数据的文件：

5
11 24 07 20 03
04 12 25 08 16
17 05 13 21 09
10 18 01 14 22
23 06 19 02 15
3
04 09 02
03 05 07
08 01 06

第一个数字表示方矩阵的大小，该数字之后的线是矩阵中用空格分隔的元素。

如何将这些数据读入向量向量？抱歉，我是编程新手。我如何确保一旦程序获得大小，它便会读取矩阵的确切行数？会有很多矩阵，因此，在将值传递给适当的函数后，如何清除向量？

我认为我所做的代码对您没有任何意义，但这是...

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.Vector;

    public class Main
    {

        public static void main(String[] args) throws Exception
        {
            FileInputStream fstream = new FileInputStream("file.txt");
            DataInputStream in = new DataInputStream(fstream);
            BufferedReader br = new BufferedReader(new InputStreamReader(in));

            Vector<Vector<Integer>> matrix = new Vector<Vector<Integer>>();
            Vector<Integer> rows = new Vector<Integer>();
            Vector<Integer> columns = new Vector<Integer>();

            String line;
            int size;

            while((line = br.readLine()) != null)
            {
                String[] temp = line.split(" ");

                for(String element: temp)
                {
                    /* This is what I was thinking:
                       If element is the only thing in the line then make it size.
                       Once you have the size, enter the data into vectors.

                       I don't know how to code these parts especially how can you put the 
                       elements in vector of vectors. Like how can I store them in rows and 
                       columns? Arrays is simple because you can say store at arr[1][2].
                     */

                    size = Integer.parseInt(element);

                    rows.add(Integer.parseInt(element));
                }
            }
        }
    }

答案

关于您的代码的评论：

• 您应使用try-with-resources。

• 删除DataInputStream。您甚至没有使用添加的内容。

• 不要使用Vector，请改用List。或建立一个int[][]，因为您知道大小。

• 不要在循环前声明rows和columns。

这里是可能的代码示例：

try (BufferedReader br = Files.newBufferedReader(Paths.get("file.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        int size = Integer.parseInt(line);

        List<List<Integer>> matrix = new ArrayList<>();
        for (int i = 0; i < size; i++) {
            if ((line = br.readLine()) == null)
                throw new EOFException();

            List<Integer> row = new ArrayList<>();
            for (String value : line.split(" "))
                row.add(Integer.parseInt(value));
            matrix.add(row);
        }

        System.out.println(matrix);
    }
}

输出

[[11, 24, 7, 20, 3], [4, 12, 25, 8, 16], [17, 5, 13, 21, 9], [10, 18, 1, 14, 22], [23, 6, 19, 2, 15]]
[[4, 9, 2], [3, 5, 7], [8, 1, 6]]

如前所述，您也可以构建2D数组：

try (BufferedReader br = Files.newBufferedReader(Paths.get("file.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        int size = Integer.parseInt(line);

        int[][] matrix = new int[size][size];
        for (int i = 0; i < size; i++) {
            if ((line = br.readLine()) == null)
                throw new EOFException();

            String[] values = line.split(" ");
            for (int j = 0; j < size; j++)
                matrix[i][j] = Integer.parseInt(values[j]);
        }

        System.out.println(Arrays.deepToString(matrix));
    }
}