# C++ Program to Interchange Elements of First and Last Columns in Matrix

20/06/2024

Interchanging elements of the first and last columns of a matrix involves swapping the elements of the first column with the corresponding elements of the last column.

Problem Statement

Given a matrix, interchange the elements of the first column with those of the last column.

Approach

1. Initialization: Verify the matrix is valid (non-empty and has more than one column).
2. Swapping Elements: Iterate through each row of the matrix and swap the elements of the first column with the corresponding elements of the last column.

Example

For a 3×3 matrix:

Matrix before interchange:

1 2 3

4 5 6

7 8 9

Matrix after interchange:

3 2 1

6 5 4

9 8 7

C++ Code Implementation

Here is a C++ program to interchange the elements of the first and last columns of a matrix:

#include <iostream>

#include <vector>

using namespace std;

// Function to interchange elements of the first and last columns of a matrix

void interchangeFirstLastColumns(vector<vector<int>>& matrix) {

int numRows = matrix.size();

int numCols = matrix[0].size();

if (numCols < 2) {

cout << “Matrix must have at least two columns to interchange.” << endl;

return;

}

for (int row = 0; row < numRows; ++row) {

swap(matrix[row][0], matrix[row][numCols – 1]);

}

}

// Function to print a matrix

void printMatrix(const vector<vector<int>>& matrix) {

for (const auto& row : matrix) {

for (const auto& elem : row) {

cout << elem << ” “;

}

cout << endl;

}

}

int main() {

// Initializing a 3×3 matrix

vector<vector<int>> matrix = {

{1, 2, 3},

{4, 5, 6},

{7, 8, 9}

};

cout << “Matrix before interchange:” << endl;

printMatrix(matrix);

// Interchanging the first and last columns

interchangeFirstLastColumns(matrix);

cout << “Matrix after interchange:” << endl;

printMatrix(matrix);

return 0;

}

Explanation

1. Function interchangeFirstLastColumns:

• Parameters: Takes a 2D vector (matrix).
• Validation: Checks if the matrix has at least two columns. If not, it outputs a message and returns.
• Swapping Elements: Uses a loop to iterate through each row, swapping the elements of the first column with the corresponding elements of the last column.
1. Function printMatrix:

• Parameters: Takes a 2D vector (matrix).
• Printing: Iterates through the matrix and prints its elements in a formatted manner for better visualization.
1. Main Function:

• Matrix Initialization: Creates a sample 3×3 matrix.
• Printing Before Interchange: Prints the matrix before interchanging the columns.
• Column Interchange: Calls the interchangeFirstLastColumns function to swap the first and last columns.
• Printing After Interchange: Prints the matrix after interchanging the columns.