How do I turn a matrix input into a multidimensional array?-CodePudding

I'm trying to figure out how to turn this type of input from scanner:

3
a b c
d e f
g h i

into this array:

String[][] arr = {{a,b,c}, {d,e,f}, {g,h i}}

The first row specifies the dimensions of the array, and the lines after are the matrix.

This is the code that I have so far:

Scanner scan = new Scanner(System.in);
int num = scan.nextInt();
scan.nextLine();

String[][] matrix = new String[num][num];

I know I'll probably need a loop that separates each entry in the row by spaces and then add it into the first row in the array, then check for a new line repeat with each row, but I can't figure out how to implement this code. I've made the program in Python, but I can't figure out how to do this in Java.

CodePudding user response：

The below code answers your question, namely processes the input as indicated in your question which is first obtaining the [square] matrix dimension followed by separate lines where each line contains all the elements for a single row of the matrix where the elements are separated by spaces.

import java.util.Arrays;
import java.util.Scanner;

public class Matrix {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);

        // Number of elements in each row and each column of matrix.
        int num = scan.nextInt();
        String[][] matrix = new String[num][num];
        scan.nextLine(); // Ignore return value.
        for (int row = 0; row < num; row  ) {

            // Enter elements for single row of matrix, delimited by spaces.
            String line = scan.nextLine();

            String[] elements = line.split("\\s ");
            for (int column = 0; column < num; column  ) {
                matrix[row][column] = elements[column]; // Note: user entered values not checked.
            }
        }
        System.out.println(Arrays.deepToString(matrix));
    }
}

Output for a sample run of the above code, using the sample values from your question:

3
a b c
d e f
g h i
[[a, b, c], [d, e, f], [g, h, i]]

CodePudding user response：

Firstly, since we are taking int rather than strings, the matrix 2d-array should be one of int.

The rest should be almost identical structurally to your python code as far as I can imagine:

...
Scanner scan = new Scanner(System.in);
int num = scan.nextInt();
int[][] matrix = new int[num][num];

scan.nextLine();
for (int i = 0; i < num; i  ) {
  for (int j = 0; j < num; j  ) {
    matrix[i][j] = scan.nextInt();
  }
  scan.nextLine();
}
...

CodePudding user response：

You can solve this problem by looping through the rows and columns in a 2D array.

import java.util.*;

class Test {
    public static void main(String[] args) {
        int row = 3, column = 3;
        String[][] matrix = new String[row][column];
        
        read(matrix, row, column);
        print(matrix, row, column);
    }
    
    public static void read(String[][] matrix, int row, int column) {
        Scanner scanner = new Scanner(System.in);
        String input;

        for(int i = 0 ; i < row ;   i) {
            for(int j = 0 ; j < column ;   j) {
                input = scanner.nextLine();
                matrix[i][j] = input;
            }
        }
    }
    
    public static void print(String[][] matrix, int row, int column) {
        for(int i = 0 ; i < row;   i) {
            for(int j = 0 ; j < column ;   j) {
                String result = String.format("MATRIX [%d][%d]: %s", i, j, matrix[i][j]);
                System.out.println(result);
            }
        }
    }
}