Print All Non-Boundary Elements of Matrix in C++

A matrix is a two-dimensional array. The elements that are present on the edges are called boundary elements, and the elements that are present inside the matrix, not present on the edges, are known as non-boundary elements. In this article, we are going to discuss how to print non-boundary elements of the matrix.

Problem Description

We are given a matrix and we have to print all non-boundary elements present in the matrix. Rows and columns are present in the matrix. The horizontal lines are called rows and the vertical lines are called columns. Below are some examples to understand the problem clearly:

Example 1

Input

1 2 3
4 5 6
7 8 9

Output

5

Example 2

Input

1  2  3  4  5  6
7  8  9  10 11 12
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30

Output

8  9  10 11
14 15 16 17
20 21 22 23
26 27 28 29

Approach

The approach involves the following steps:

• Check if the matrix has only one row or one column. If true, then there are no boundary elements in the matrix.
• Identify the boundary elements:
  For rows, the boundary elements are present in the first row (row 0) or the last row (row = rows - 1).
  For columns, the boundary elements are present in the first column (column 0) or the last column (column = columns - 1).
• Traverse the matrix and print only the non-boundary elements, skipping the identified boundary elements.

C++ program to print all non-boundary elements of matrix

#include <bits/stdc++.h>
using namespace std;

void nonBoundaryElements(int rows, int cols, int matrix[5][6]) {
    // Check edge case
    if (rows < 3 || cols < 3) {
        cout << "No non-boundary elements exist in the matrix." << endl;
        return;
    }
    // Skip row elements
    for (int i = 1; i < rows - 1; i++) {
        // Skip column elements
        for (int j = 1; j < cols - 1; j++) {
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
}

int main() {
    int rows = 5, cols = 6;
    int matrix[5][6] = {
        {1, 2, 3, 4, 5, 6},
        {7, 8, 9, 10, 11, 12},
        {13, 14, 15, 16, 17, 18},
        {19, 20, 21, 22, 23, 24},
        {25, 26, 27, 28, 29, 30}
    };

    // Print the non-boundary elements
    cout << "Non-boundary elements of the matrix are:" << endl;
    nonBoundaryElements(rows, cols, matrix);

    return 0;
}
    

Output

Non-boundary elements of the matrix are:
8  9  10 11
14 15 16 17
20 21 22 23

Time and Space Complexities

Time Complexity: O(rows × columns), as we are traversing the rows and columns except the boundary elements.

Space Complexity: O(1), as we are not using any data structure.