# Program to print the Diagonals of a Matrix

• Difficulty Level : Basic
• Last Updated : 20 Apr, 2021

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

Examples :

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```Input:
4
1 2 3 4
4 3 2 1
7 8 9 6
6 5 4 3
Output:
Principal Diagonal: 1, 3, 9, 3
Secondary Diagonal: 4, 2, 8, 6

Input:
3
1 1 1
1 1 1
1 1 1
Output:
Principal Diagonal: 1, 1, 1
Secondary Diagonal: 1, 1, 1```

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

```A00 A01 A02 A03
A10 A11 A12 A13
A20 A21 A22 A23
A30 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.

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