# Program to print the Diagonals of a Matrix

Given a 2D square matrix, print the Principal and Secondary diagonals.

Examples :

`Input: 41 2 3 44 3 2 17 8 9 66 5 4 3Output:Principal Diagonal: 1, 3, 9, 3Secondary Diagonal: 4, 2, 8, 6Input:31 1 11 1 11 1 1Output:Principal Diagonal: 1, 1, 1Secondary Diagonal: 1, 1, 1`

For example, consider the following 4 X 4 input matrix.

`A00 A01 A02 A03A10 A11 A12 A13A20 A21 A22 A23A30 A31 A32 A33`
• The primary diagonal is formed by the elements A00, A11, A22, A33.
Condition for Principal Diagonal:
`The row-column condition is row = column.`
• The secondary diagonal is formed by the elements A03, A12, A21, A30.
Condition for Secondary Diagonal:
`The row-column condition is row = numberOfRows - column -1.`

Method 1:
In this method, we use two loops i.e. a loop for columns and a loop for rows and in the inner loop we check for the condition stated above.

## C++

 `// C++ Program to print the Diagonals of a Matrix`   `#include ` `using` `namespace` `std;`   `const` `int` `MAX = 100;`   `// Function to print the Principal Diagonal` `void` `printPrincipalDiagonal(``int` `mat[][MAX], ``int` `n)` `{` `    ``cout << ``"Principal Diagonal: "``;`   `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``for` `(``int` `j = 0; j < n; j++) {`   `            ``// Condition for principal diagonal` `            ``if` `(i == j)` `                ``cout << mat[i][j] << ``", "``;` `        ``}` `    ``}` `    ``cout << endl;` `}`   `// Function to print the Secondary Diagonal` `void` `printSecondaryDiagonal(``int` `mat[][MAX], ``int` `n)` `{` `    ``cout << ``"Secondary Diagonal: "``;`   `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``for` `(``int` `j = 0; j < n; j++) {`   `            ``// Condition for secondary diagonal` `            ``if` `((i + j) == (n - 1))` `                ``cout << mat[i][j] << ``", "``;` `        ``}` `    ``}` `    ``cout << endl;` `}`   `// Driver code` `int` `main()` `{` `    ``int` `n = 4;` `    ``int` `a[][MAX] = { { 1, 2, 3, 4 },` `                     ``{ 5, 6, 7, 8 },` `                     ``{ 1, 2, 3, 4 },` `                     ``{ 5, 6, 7, 8 } };`   `    ``printPrincipalDiagonal(a, n);` `    ``printSecondaryDiagonal(a, n);` `    ``return` `0;` `}`

## Java

 `// Java Program to print the Diagonals of a Matrix` `class` `GFG {` `    ``static` `int` `MAX = ``100``;`   `    ``// Function to print the Principal Diagonal` `    ``static` `void` `printPrincipalDiagonal(``int` `mat[][], ``int` `n)` `    ``{` `        ``System.out.print(``"Principal Diagonal: "``);`   `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``for` `(``int` `j = ``0``; j < n; j++) {`   `                ``// Condition for principal diagonal` `                ``if` `(i == j) {` `                    ``System.out.print(mat[i][j] + ``", "``);` `                ``}` `            ``}` `        ``}` `        ``System.out.println(``""``);` `    ``}`   `    ``// Function to print the Secondary Diagonal` `    ``static` `void` `printSecondaryDiagonal(``int` `mat[][], ``int` `n)` `    ``{` `        ``System.out.print(``"Secondary Diagonal: "``);`   `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``for` `(``int` `j = ``0``; j < n; j++) {`   `                ``// Condition for secondary diagonal` `                ``if` `((i + j) == (n - ``1``)) {` `                    ``System.out.print(mat[i][j] + ``", "``);` `                ``}` `            ``}` `        ``}` `        ``System.out.println(``""``);` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String args[])` `    ``{` `        ``int` `n = ``4``;` `        ``int` `a[][] = { { ``1``, ``2``, ``3``, ``4` `},` `                      ``{ ``5``, ``6``, ``7``, ``8` `},` `                      ``{ ``1``, ``2``, ``3``, ``4` `},` `                      ``{ ``5``, ``6``, ``7``, ``8` `} };`   `        ``printPrincipalDiagonal(a, n);` `        ``printSecondaryDiagonal(a, n);` `    ``}` `}`   `// This code is contributed by Rajput-Ji`

## Python3

 `# Python3 Program to print the Diagonals of a Matrix` `MAX` `=` `100`   `# Function to print the Principal Diagonal` `def` `printPrincipalDiagonal(mat, n):` `    ``print``(``"Principal Diagonal: "``, end ``=` `"")`   `    ``for` `i ``in` `range``(n):` `        ``for` `j ``in` `range``(n):`   `            ``# Condition for principal diagonal` `            ``if` `(i ``=``=` `j):` `                ``print``(mat[i][j], end ``=` `", "``)` `    ``print``()`   `# Function to print the Secondary Diagonal` `def` `printSecondaryDiagonal(mat, n):` `    ``print``(``"Secondary Diagonal: "``, end ``=` `"")`   `    ``for` `i ``in` `range``(n):` `        ``for` `j ``in` `range``(n):`   `            ``# Condition for secondary diagonal` `            ``if` `((i ``+` `j) ``=``=` `(n ``-` `1``)):` `                ``print``(mat[i][j], end ``=` `", "``)` `    ``print``()`   `# Driver code` `n ``=` `4` `a ``=` `[[ ``1``, ``2``, ``3``, ``4` `],` `     ``[ ``5``, ``6``, ``7``, ``8` `],` `     ``[ ``1``, ``2``, ``3``, ``4` `],` `     ``[ ``5``, ``6``, ``7``, ``8` `]]`   `printPrincipalDiagonal(a, n)` `printSecondaryDiagonal(a, n)`   `# This code is contributed by Mohit Kumar`

## C#

 `// C# Program to print the Diagonals of a Matrix` `using` `System;`   `class` `GFG {` `    ``static` `int` `MAX = 100;`   `    ``// Function to print the Principal Diagonal` `    ``static` `void` `printPrincipalDiagonal(``int``[, ] mat, ``int` `n)` `    ``{` `        ``Console.Write(``"Principal Diagonal: "``);`   `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``for` `(``int` `j = 0; j < n; j++) {`   `                ``// Condition for principal diagonal` `                ``if` `(i == j) {` `                    ``Console.Write(mat[i, j] + ``", "``);` `                ``}` `            ``}` `        ``}` `        ``Console.WriteLine(``""``);` `    ``}`   `    ``// Function to print the Secondary Diagonal` `    ``static` `void` `printSecondaryDiagonal(``int``[, ] mat, ``int` `n)` `    ``{` `        ``Console.Write(``"Secondary Diagonal: "``);`   `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``for` `(``int` `j = 0; j < n; j++) {`   `                ``// Condition for secondary diagonal` `                ``if` `((i + j) == (n - 1)) {` `                    ``Console.Write(mat[i, j] + ``", "``);` `                ``}` `            ``}` `        ``}` `        ``Console.WriteLine(``""``);` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `Main(String[] args)` `    ``{` `        ``int` `n = 4;` `        ``int``[, ] a = { { 1, 2, 3, 4 },` `                      ``{ 5, 6, 7, 8 },` `                      ``{ 1, 2, 3, 4 },` `                      ``{ 5, 6, 7, 8 } };`   `        ``printPrincipalDiagonal(a, n);` `        ``printSecondaryDiagonal(a, n);` `    ``}` `}`   `// This code is contributed by 29AjayKumar`

## Javascript

 ``

Output

```Principal Diagonal: 1, 6, 3, 8,
Secondary Diagonal: 4, 7, 2, 5,

```

Complexity Analysis:

• Time Complexity: O(n2).
As there is a nested loop involved so the time complexity is squared.
• Auxiliary Space: O(1).
As no extra space is occupied.

Method 2:
In this method, the same condition for printing the diagonal elements can be achieved using a single for loop.
Approach:

1. For Principal Diagonal elements: Run a for a loop until n, where n is the number of columns, and print array[i][i] where i is the index variable.
2. For Secondary Diagonal elements: Run a for a loop until n, where n is the number of columns and print array[i][k] where i is the index variable and k = array_length – 1. Decrease k until i < n.

Below is the implementation of the above approach.

## C++

 `// C++ Program to print the Diagonals of a Matrix`   `#include ` `using` `namespace` `std;`   `const` `int` `MAX = 100;`   `// Function to print the Principal Diagonal` `void` `printPrincipalDiagonal(``int` `mat[][MAX], ``int` `n)` `{` `    ``cout << ``"Principal Diagonal: "``;`   `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// Printing principal diagonal` `        ``cout << mat[i][i] << ``", "``;` `    ``}` `    ``cout << endl;` `}`   `// Function to print the Secondary Diagonal` `void` `printSecondaryDiagonal(``int` `mat[][MAX], ``int` `n)` `{` `    ``cout << ``"Secondary Diagonal: "``;` `    ``int` `k = n - 1;` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// Printing secondary diagonal` `        ``cout << mat[i][k--] << ``", "``;` `    ``}` `    ``cout << endl;` `}`   `// Driver code` `int` `main()` `{` `    ``int` `n = 4;` `    ``int` `a[][MAX] = { { 1, 2, 3, 4 },` `                     ``{ 5, 6, 7, 8 },` `                     ``{ 1, 2, 3, 4 },` `                     ``{ 5, 6, 7, 8 } };`   `    ``printPrincipalDiagonal(a, n);` `    ``printSecondaryDiagonal(a, n);` `    ``return` `0;` `}`   `// This code is contributed by yashbeersingh42`

## Java

 `// Java Program to print the ` `// Diagonals of a Matrix` `class` `Main{` `  `  `static` `int` `MAX = ``100``;` `    `  `// Function to print the Principal Diagonal` `public` `static` `void` `printPrincipalDiagonal(``int` `mat[][], ` `                                          ``int` `n)` `{` `  ``System.out.print(``"Principal Diagonal: "``);`   `  ``for` `(``int` `i = ``0``; i < n; i++) ` `  ``{` `    ``// Printing principal diagonal` `    ``System.out.print(mat[i][i] + ``", "``);` `  ``}` `  ``System.out.println();` `}`   `// Function to print the Secondary Diagonal` `public` `static` `void` `printSecondaryDiagonal(``int` `mat[][], ` `                                          ``int` `n)` `{` `  ``System.out.print(``"Secondary Diagonal: "``);` `  ``int` `k = n - ``1``;` `  `  `  ``for` `(``int` `i = ``0``; i < n; i++) ` `  ``{` `    ``// Printing secondary diagonal` `    ``System.out.print(mat[i][k--] + ``", "``);` `  ``}` `  ``System.out.println();` `}`   `public` `static` `void` `main(String[] args) ` `{` `  ``int` `n = ``4``;` `  ``int` `a[][] = {{``1``, ``2``, ``3``, ``4``},` `               ``{``5``, ``6``, ``7``, ``8``},` `               ``{``1``, ``2``, ``3``, ``4``},` `               ``{``5``, ``6``, ``7``, ``8``}};` `  ``printPrincipalDiagonal(a, n);` `  ``printSecondaryDiagonal(a, n);` `}` `}`   `// This code is contributed by divyeshrabadiya07`

## Python3

 `# Python3 program to print the` `# Diagonals of a Matrix` `MAX` `=` `100`   `# Function to print the Principal Diagonal` `def` `printPrincipalDiagonal(mat, n):`   `    ``print``(``"Principal Diagonal: "``, end ``=` `"")`   `    ``for` `i ``in` `range``(n):` `        `  `        ``# Printing principal diagonal` `        ``print``(mat[i][i], end ``=` `", "``)`   `    ``print``()`   `# Function to print the Secondary Diagonal` `def` `printSecondaryDiagonal(mat, n):`   `    ``print``(``"Secondary Diagonal: "``, end ``=` `"")` `    ``k ``=` `n ``-` `1` `    `  `    ``for` `i ``in` `range``(n):` `        `  `        ``# Printing secondary diagonal` `        ``print``(mat[i][k], end ``=` `", "``)` `        ``k ``-``=` `1`   `    ``print``()` `    `  `# Driver Code` `n ``=` `4` `a ``=` `[ [ ``1``, ``2``, ``3``, ``4` `],` `      ``[ ``5``, ``6``, ``7``, ``8` `],` `      ``[ ``1``, ``2``, ``3``, ``4` `],` `      ``[ ``5``, ``6``, ``7``, ``8` `] ]`   `printPrincipalDiagonal(a, n)` `printSecondaryDiagonal(a, n)`   `# This code is contributed by divyesh072019`

## C#

 `// C# program for the ` `// above approach` `using` `System;` `class` `GFG{` `    `  `// Function to print the ` `// Principal Diagonal` `static` `void` `printPrincipalDiagonal(``int` `[,]mat, ` `                                   ``int` `n)` `{` `  ``Console.Write(``"Principal Diagonal: "``);`   `  ``for` `(``int` `i = 0; i < n; i++) ` `  ``{` `    ``// Printing principal diagonal` `    ``Console.Write(mat[i, i] + ``", "``);` `  ``}` `  ``Console.Write(``"\n"``);` `}` ` `  `// Function to print the ` `// Secondary Diagonal` `static` `void` `printSecondaryDiagonal(``int` `[,]mat, ` `                                   ``int` `n)` `{` `  ``Console.Write(``"Secondary Diagonal: "``);` `  ``int` `k = n - 1;` `  `  `  ``for` `(``int` `i = 0; i < n; i++) ` `  ``{` `    ``// Printing secondary diagonal` `    ``Console.Write(mat[i, k--] + ``", "``);` `  ``}` `  `  `  ``Console.Write(``"\n"``);` `}` `    `  `    `  `// Driver code` `static` `void` `Main() ` `{` `  ``int` `n = 4;` `  ``int` `[,]a = {{1, 2, 3, 4},` `              ``{5, 6, 7, 8},` `              ``{1, 2, 3, 4},` `              ``{5, 6, 7, 8}};` `  ``printPrincipalDiagonal(a, n);` `  ``printSecondaryDiagonal(a, n);` `}` `}`   `// This code is contributed by rutvik_56`

## Javascript

 ``

Output

```Principal Diagonal: 1, 6, 3, 8,
Secondary Diagonal: 4, 7, 2, 5,

```

Complexity Analysis:

• Time Complexity: O(n).
As there is only one loop involved so the time complexity is linear.
• Auxiliary Space: O(1).
As no extra space is occupied.

### Using list comprehensions:

Approach:

Define a function print_diagonals that takes a 2D list (matrix) as input.
Get the length of the matrix and store it in the variable n.
Use a list comprehension to create a list of the principal diagonal elements. To do this, iterate over the range from 0 to n and for each index i, append matrix[i][i] to the list principal.
Print the list of principal diagonal elements using the join() method to convert the list to a string separated by commas.
Use another list comprehension to create a list of the secondary diagonal elements. To do this, iterate over the range from 0 to n and for each index i, append matrix[i][n-1-i] to the list secondary.
Print the list of secondary diagonal elements using the join() method to convert the list to a string separated by commas.
Example usage: Create a 2D list matrix, call the print_diagonals function with matrix as input.

## C++

 `#include ` `#include `   `// Function to print the principal and secondary diagonals` `// of a matrix` `void` `printDiagonals(std::vector >& matrix)` `{` `    ``int` `n` `        ``= matrix` `              ``.size(); ``// Get the size of the square matrix`   `    ``// Get the principal diagonal` `    ``std::vector<``int``> principal(n);` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``principal[i] = matrix[i][i];` `    ``}`   `    ``// Print the principal diagonal` `    ``std::cout << ``"Principal Diagonal: "``;` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``std::cout << principal[i];` `        ``if` `(i != n - 1) {` `            ``std::cout << ``", "``;` `        ``}` `    ``}` `    ``std::cout << std::endl;`   `    ``// Get the secondary diagonal` `    ``std::vector<``int``> secondary(n);` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``secondary[i] = matrix[i][n - 1 - i];` `    ``}`   `    ``// Print the secondary diagonal` `    ``std::cout << ``"Secondary Diagonal: "``;` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``std::cout << secondary[i];` `        ``if` `(i != n - 1) {` `            ``std::cout << ``", "``;` `        ``}` `    ``}` `    ``std::cout << std::endl;` `}`   `int` `main()` `{` `    ``std::vector > matrix` `        ``= { { 1, 2, 3, 4 },` `            ``{ 4, 3, 2, 1 },` `            ``{ 7, 8, 9, 6 },` `            ``{ 6, 5, 4, 3 } };`   `    ``printDiagonals(matrix);`   `    ``return` `0;` `}`

## Java

 `import` `java.io.*;` `public` `class` `GFG {` `    ``public` `static` `void` `printDiagonals(``int``[][] matrix) {` `        ``int` `n = matrix.length;` `        ``// Get the principal diagonal` `        ``int``[] principal = ``new` `int``[n];` `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``principal[i] = matrix[i][i];` `        ``}` `        ``System.out.print(``"Principal Diagonal: "``);` `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``System.out.print(principal[i]);` `            ``if` `(i != n - ``1``) {` `                ``System.out.print(``", "``);` `            ``}` `        ``}` `        ``System.out.println();` `        ``// Get the secondary diagonal` `        ``int``[] secondary = ``new` `int``[n];` `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``secondary[i] = matrix[i][n - ``1` `- i];` `        ``}` `        ``System.out.print(``"Secondary Diagonal: "``);` `        ``for` `(``int` `i = ``0``; i < n; i++) {` `            ``System.out.print(secondary[i]);` `            ``if` `(i != n - ``1``) {` `                ``System.out.print(``", "``);` `            ``}` `        ``}` `        ``System.out.println();` `    ``}` `    ``public` `static` `void` `main(String[] args) {` `        ``int``[][] matrix = {` `            ``{``1``, ``2``, ``3``, ``4``},` `            ``{``4``, ``3``, ``2``, ``1``},` `            ``{``7``, ``8``, ``9``, ``6``},` `            ``{``6``, ``5``, ``4``, ``3``}` `        ``};` `        ``printDiagonals(matrix);` `    ``}` `}`

## Python3

 `def` `print_diagonals(matrix):` `    ``n ``=` `len``(matrix)` `    ``# Get the principal diagonal` `    ``principal ``=` `[matrix[i][i] ``for` `i ``in` `range``(n)]` `    ``print``(``"Principal Diagonal:"``, ``", "``.join(``map``(``str``, principal)))` `    ``# Get the secondary diagonal` `    ``secondary ``=` `[matrix[i][n``-``1``-``i] ``for` `i ``in` `range``(n)]` `    ``print``(``"Secondary Diagonal:"``, ``", "``.join(``map``(``str``, secondary)))`   `# Example usage` `matrix ``=` `[[``1``, ``2``, ``3``, ``4``], [``4``, ``3``, ``2``, ``1``], [``7``, ``8``, ``9``, ``6``], [``6``, ``5``, ``4``, ``3``]]` `print_diagonals(matrix)`

## C#

 `using` `System;`   `public` `class` `GFG {` `    ``public` `static` `void` `PrintDiagonals(``int``[,] matrix) {` `        ``int` `n = matrix.GetLength(0);` `        `  `        ``// Get the principal diagonal` `        ``int``[] principal = ``new` `int``[n];` `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``principal[i] = matrix[i, i];` `        ``}` `        `  `        ``Console.Write(``"Principal Diagonal: "``);` `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``Console.Write(principal[i]);` `            ``if` `(i != n - 1) {` `                ``Console.Write(``", "``);` `            ``}` `        ``}` `        ``Console.WriteLine();` `        `  `        ``// Get the secondary diagonal` `        ``int``[] secondary = ``new` `int``[n];` `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``secondary[i] = matrix[i, n - 1 - i];` `        ``}` `        `  `        ``Console.Write(``"Secondary Diagonal: "``);` `        ``for` `(``int` `i = 0; i < n; i++) {` `            ``Console.Write(secondary[i]);` `            ``if` `(i != n - 1) {` `                ``Console.Write(``", "``);` `            ``}` `        ``}` `        ``Console.WriteLine();` `    ``}` `    `  `    ``public` `static` `void` `Main(``string``[] args) {` `        ``int``[,] matrix = {` `            ``{1, 2, 3, 4},` `            ``{4, 3, 2, 1},` `            ``{7, 8, 9, 6},` `            ``{6, 5, 4, 3}` `        ``};` `        `  `        ``PrintDiagonals(matrix);` `    ``}` `}`

## Javascript

 `function` `print_diagonals(matrix) {` `    ``let n = matrix.length;` `    ``// Get the principal diagonal` `    ``let principal = [];` `    ``for` `(let i = 0; i < n; i++) {` `        ``principal.push(matrix[i][i]);` `    ``}` `    ``console.log(``"Principal Diagonal:"``, principal.join(``", "``));` `    ``// Get the secondary diagonal` `    ``let secondary = [];` `    ``for` `(let i = 0; i < n; i++) {` `        ``secondary.push(matrix[i][n - 1 - i]);` `    ``}` `    ``console.log(``"Secondary Diagonal:"``, secondary.join(``", "``));` `}`   `// Example usage` `let matrix = [` `    ``[1, 2, 3, 4],` `    ``[4, 3, 2, 1],` `    ``[7, 8, 9, 6],` `    ``[6, 5, 4, 3]` `];` `print_diagonals(matrix);`

Output

```Principal Diagonal: 1, 3, 9, 3
Secondary Diagonal: 4, 2, 8, 6

```

The time complexity of this approach is also O(n^2)

The auxiliary space is O(n).

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