How to find the boundary elements of a matrix

Boundary elements of a matrix

The boundary elements of a matrix are found at the boundary of the matrix.

For example, consider the matrix below.

[1, 2, 3, 4]
[4, 5, 6, 5]
[7, 8, 9, 6]

The boundary elements of the matrix are as follows.

1 2 3 4 
4     5 
7 8 9 6

The following image offers a visual representation for clarity.

Algorithm

Run two loops. One loop iterates along the rows, and the other iterates along the columns. During the iteration, execute the following steps:
1. If the row number is either zero or the last rowthe number of rows = 1, print the element at the current position.
2. If the column number is either zero or the last columnthe number of columns = 1, print the element at the current position.

Time complexity: O(N*N)
Space complexity: O(1)

Code

The code below finds the boundary elements of a matrix and displays the boundary element in output.

import java.util.Arrays;
public class Main{
    private static void printBoundaryElements(int[][] matrix){
        // get the number of rows in the matrix
        int numRows = matrix.length;
        // get the number of columns in the matrix
        int numCols = matrix[0].length;
        // Loop through every row in the matrix
        for(int i = 0; i < numRows; i++)
        {
            // Loop through every column in the matrix
            for(int j = 0; j < numCols; j++)
            {
                // check whether the condition for boundary element is true
                if (i == 0 || j == 0 || i == numRows - 1  || j == numCols - 1)
                    System.out.print(matrix[i][j] + " ");
                else
                    System.out.print("  ");
            }
            System.out.println();
        }
    }
    private static void printMatrix(int[][] matrix){
        for (int[] row : matrix)
            System.out.println(Arrays.toString(row));
    }
    public static void main(String[] args){
        int matrix[][] = {{1, 2, 3, 4},
                {4, 5, 6, 5},
                {7, 8 , 9, 6}
        };
        printMatrix(matrix);
        System.out.println("The boundary elements of the above matrix is as follows:");
        printBoundaryElements(matrix);
    }
}

Boundary elements of the matrix

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)

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