将 .txt 文件读入二维数组

Question

There are a few of these topics out there, but this problem has a slight twist that makes it different.

I'm focused on only half of a larger problem. I'm sure many of you are aware of the magic square problem.

Prompt:
Assume a file with lines and numbers on each line like the square shown. Write a program that reads info into a two dimensional array of intS. The program should determine if the matrix is a magic square or not.

Working Solution:

public static int[][] create2DIntMatrixFromFile(String filename) throws Exception {
int[][] matrix = {{1}, {2}};

File inFile = new File(filename);
Scanner in = new Scanner(inFile);

int intLength = 0;
String[] length = in.nextLine().trim().split("\\s+");
  for (int i = 0; i < length.length; i++) {
    intLength++;
  }

in.close();

matrix = new int[intLength][intLength];
in = new Scanner(inFile);

int lineCount = 0;
while (in.hasNextLine()) {
  String[] currentLine = in.nextLine().trim().split("\\s+"); 
     for (int i = 0; i < currentLine.length; i++) {
        matrix[lineCount][i] = Integer.parseInt(currentLine[i]);    
            }
  lineCount++;
 }                                 
 return matrix;
}


public static boolean isMagicSquare(int[][] square) {

  return false;
}

Here is my (old) code for reading info from a text file into a 2D array:

public static int[][] create2DIntMatrixFromFile(String filename) throws Exception {
    int[][] matrix = {{1}, {2}};
    File inFile = new File(filename);
    Scanner in = new Scanner(inFile);
    in.useDelimiter("[/n]");

    String line = "";
    int lineCount = 0;

    while (in.hasNextLine()) {
        line = in.nextLine().trim();
        Scanner lineIn = new Scanner(line);
        lineIn.useDelimiter("");

        for (int i = 0; lineIn.hasNext(); i++) {
            matrix[lineCount][i] = Integer.parseInt(lineIn.next());
            lineIn.next();
        }

        lineCount++;
    }

    return matrix;
}

public static boolean isMagicSquare(int[][] square) {
    return false;
}

And here is the text file I am reading from. It is in the shape of a 9x9 2D array, but the program must accommodate an array of ambiguous size.

  37  48  59  70  81   2  13  24  35 
  36  38  49  60  71  73   3  14  25 
  26  28  39  50  61  72  74   4  15 
  16  27  29  40  51  62  64  75   5 
   6  17  19  30  41  52  63  65  76 
  77   7  18  20  31  42  53  55  66 
  67  78   8  10  21  32  43  54  56 
  57  68  79   9  11  22  33  44  46 
  47  58  69  80   1  12  23  34  45 

There are two spaces proceeding each line on purpose.

Before I state the exact problem, this is a homework template so the method declaration and variable initialization was pre-determined.

I'm not positive that the method even correctly creates a 2D Array from the file because I can't run it yet. The issue is that for some reason "matrix" was initialized with 1 column and 2 rows. For what reason I'm not sure, but in order to fill an array with the numbers from the file I need to create a 2D array with dimensions equal to the number of values in a line.

I previously had written code to create a new 2D array

int[line.length()][line.length()]

but it created a 36x36 array because that's how many individual characters are in one line. I have a feeling it's as simple as looping through the first line and having a counter keep track of each sequence of numbers separated by a zero.

To me, that solution seems too inefficient and time consuming just to find the dimensions of the new array. What's the best way to accomplish this? Without using ArrayLists as I have to rewrite this program after using ArrayLists.

Answer 1

I produced the following 2D array from the file you provided:

 37 | 48 | 59 | 70 | 81 |  2 | 13 | 24 | 35
----+----+----+----+----+----+----+----+----
 36 | 38 | 49 | 60 | 71 | 73 |  3 | 14 | 25
----+----+----+----+----+----+----+----+----
 26 | 28 | 39 | 50 | 61 | 72 | 74 |  4 | 15
----+----+----+----+----+----+----+----+----
 16 | 27 | 29 | 40 | 51 | 62 | 64 | 75 |  5
----+----+----+----+----+----+----+----+----
  6 | 17 | 19 | 30 | 41 | 52 | 63 | 65 | 76
----+----+----+----+----+----+----+----+----
 77 |  7 | 18 | 20 | 31 | 42 | 53 | 55 | 66
----+----+----+----+----+----+----+----+----
 67 | 78 |  8 | 10 | 21 | 32 | 43 | 54 | 56
----+----+----+----+----+----+----+----+----
 57 | 68 | 79 |  9 | 11 | 22 | 33 | 44 | 46
----+----+----+----+----+----+----+----+----
 47 | 58 | 69 | 80 |  1 | 12 | 23 | 34 | 45

The array figures out the size of the square when it reads the first line of the file. This is very dynamic. Its works as long as the input file is a perfect square. I have no further error handling.

Here is a simple approach which should adhere to your guidelines.

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;

public class ReadMagicSquare {
    public static int[][] create2DIntMatrixFromFile(String filename) throws Exception {
        int[][] matrix = null;

        // If included in an Eclipse project.
        InputStream stream = ClassLoader.getSystemResourceAsStream(filename);
        BufferedReader buffer = new BufferedReader(new InputStreamReader(stream));

        // If in the same directory - Probably in your case...
        // Just comment out the 2 lines above this and uncomment the line
        // that follows.
        //BufferedReader buffer = new BufferedReader(new FileReader(filename));

        String line;
        int row = 0;
        int size = 0;

        while ((line = buffer.readLine()) != null) {
            String[] vals = line.trim().split("\\s+");

            // Lazy instantiation.
            if (matrix == null) {
                size = vals.length;
                matrix = new int[size][size];
            }

            for (int col = 0; col < size; col++) {
                matrix[row][col] = Integer.parseInt(vals[col]);
            }

            row++;
        }

        return matrix;
    }

    public static void printMatrix(int[][] matrix) {
        String str = "";
        int size = matrix.length;

        if (matrix != null) {
            for (int row = 0; row < size; row++) {
                str += " ";
                for (int col = 0; col < size; col++) {
                    str += String.format("%2d",  matrix[row][col]);
                    if (col < size - 1) {
                        str += " | ";
                    }
                }
                if (row < size - 1) {
                    str += "\n";
                    for (int col = 0; col < size; col++) {
                        for (int i = 0; i < 4; i++) {
                            str += "-";
                        }
                        if (col < size - 1) {
                            str += "+";
                        }
                    }
                    str += "\n";
                } else {
                    str += "\n";
                }
            }
        }

        System.out.println(str);
    }

    public static void main(String[] args) {
        int[][] matrix = null;

        try {
            matrix = create2DIntMatrixFromFile("square.txt");
        } catch (Exception e) {
            e.printStackTrace();
        }

        printMatrix(matrix);
    }
}

This approach is more refined and optimized.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class ReadMagicSquare {

    private int[][] matrix;
    private int size = -1;
    private int log10 = 0;
    private String numberFormat;

    public ReadMagicSquare(String filename) {
        try {
            readFile(filename);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void readFile(String filename) throws IOException {
        // If included in an Eclipse project.
        InputStream stream = ClassLoader.getSystemResourceAsStream(filename);
        BufferedReader buffer = new BufferedReader(new InputStreamReader(stream));

        // If in the same directory - Probably in your case...
        // Just comment out the 2 lines above this and uncomment the line
        // that follows.
        //BufferedReader buffer = new BufferedReader(new FileReader(filename));

        String line;
        int row = 0;

        while ((line = buffer.readLine()) != null) {
            String[] vals = line.trim().split("\\s+");

            // Lazy instantiation.
            if (matrix == null) {
                size = vals.length;
                matrix = new int[size][size];
                log10 = (int) Math.floor(Math.log10(size * size)) + 1;
                numberFormat = String.format("%%%dd", log10);
            }

            for (int col = 0; col < size; col++) {
                matrix[row][col] = Integer.parseInt(vals[col]);
            }

            row++;
        }
    }

    @Override
    public String toString() {
        StringBuffer buff = new StringBuffer();

        if (matrix != null) {
            for (int row = 0; row < size; row++) {
                buff.append(" ");
                for (int col = 0; col < size; col++) {
                    buff.append(String.format(numberFormat,  matrix[row][col]));
                    if (col < size - 1) {
                        buff.append(" | ");
                    }
                }
                if (row < size - 1) {
                    buff.append("\n");
                    for (int col = 0; col < size; col++) {
                        for (int i = 0; i <= log10 + 1; i++) {
                            buff.append("-");
                        }
                        if (col < size - 1) {
                            buff.append("+");
                        }
                    }
                    buff.append("\n");
                } else {
                    buff.append("\n");
                }
            }
        }

        return buff.toString();
    }

    public static void main(String[] args) {
        ReadMagicSquare square = new ReadMagicSquare("square.txt");
        System.out.println(square.toString());
    }
}

Answer 2

You're close, but change your while loop to look like the following:

while (in.hasNextLine()) {
    Scanner lineIn = new Scanner(line);
    //The initial case - this first line is used to determine the size of the array
    if(lineIn.hasNext()) {
        //Create a String array by splitting by spaces
        String[] s = lineIn.nextLine().split(" ");
        //Reinitialize the array to hold all of your subarrays
        matrix = new int[s.length];
        for (int i = 0; i < s.length; i++) {
            //Reinitialize each subarray to hold the numbers
            matrix[i] = new int[i];
            //Finally, parse your data from the String array
            matrix[0][i] = Integer.parseInt(s[i]);
        }
    }
    //Repeat the steps now that all of your arrays have been initialized
    for (int j = 1; j < matrix.length; j++) {
        String[] s = lineIn.nextLine().split(" ");
        for (int i = 0; i < s.length; i++) {
            matrix[j][i] = Integer.parseInt(s[i]);
        }
    }
}

The biggest change that you can make to make this easier on yourself is to get your numbers line-by-line. With each line you get, it's easy to then split it into a String array so that you can parse each number separately. Doing it this way you can then get the full length of the array all at once without having to have troublesome counters.

Answer 3

First, test out the Scanner results. I don't think those delimiters will work. (BTW, Scanner's nextInt() method is handy.)

If you can assume the input is a square matrix, scanning the first line will reveal how many integers it contains. Then you can (re)allocate the arrays. Then process all the lines, including the first line that you already scanned.

Then you can set matrix = new int[n][n];

Answer 4

With Java 8 and it's Streams :

  static public int[][] create2DIntMatrixFromFile(Path path) throws IOException {
    return Files.lines(path)
      .map((l)->l.trim().split("\\s+"))
      .map((sa)->Stream.of(sa).mapToInt(Integer::parseInt).toArray())
      .toArray(int[][]::new);
  }

This is just for the 'reading' part of the question.