Program to print the Diagonals of a Matrix

20 Apr, 2021
Given a 2D square matrix, print the Principal and Secondary diagonals. 
Examples : 
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++
Java
Python3
C#
Javascript
// C++ Program to print the Diagonals of a Matrix #include <bits/stdc++.h>using namespace std; const int MAX = 100; // Function to print the Principal Diagonalvoid 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 Diagonalvoid 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 codeint 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 Program to print the Diagonals of a Matrixclass 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 Program to print the Diagonals of a MatrixMAX = 100 # Function to print the Principal Diagonaldef 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 Diagonaldef 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 coden = 4a = [[ 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# Program to print the Diagonals of a Matrixusing 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
<script>     // Javascript Program to print the Diagonals of a Matrix         let MAX = 100;      // Function to print the Principal Diagonal    function printPrincipalDiagonal(mat, n)    {        document.write("Principal Diagonal: ");          for (let i = 0; i < n; i++) {            for (let j = 0; j < n; j++) {                  // Condition for principal diagonal                if (i == j) {                    document.write(mat[i][j] + ", ");                }            }        }        document.write("</br>");    }      // Function to print the Secondary Diagonal    function printSecondaryDiagonal(mat, n)    {        document.write("Secondary Diagonal: ");          for (let i = 0; i < n; i++) {            for (let j = 0; j < n; j++) {                  // Condition for secondary diagonal                if ((i + j) == (n - 1)) {                    document.write(mat[i][j] + ", ");                }            }        }        document.write("</br>");    }         let n = 4;    let a = [ [ 1, 2, 3, 4 ],              [ 5, 6, 7, 8 ],              [ 1, 2, 3, 4 ],              [ 5, 6, 7, 8 ] ];     printPrincipalDiagonal(a, n);    printSecondaryDiagonal(a, n);     </script>
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: 
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.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.
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.
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++
Java
Python3
C#
Javascript
// C++ Program to print the Diagonals of a Matrix #include <bits/stdc++.h>using namespace std; const int MAX = 100; // Function to print the Principal Diagonalvoid 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 Diagonalvoid 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 codeint 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 Program to print the// Diagonals of a Matrixclass Main{   static int MAX = 100;     // Function to print the Principal Diagonalpublic 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 Diagonalpublic 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 program to print the# Diagonals of a MatrixMAX = 100 # Function to print the Principal Diagonaldef 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 Diagonaldef 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 Coden = 4a = [ [ 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# program for the// above approachusing System;class GFG{     // Function to print the// Principal Diagonalstatic 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 Diagonalstatic 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 codestatic 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
<script>     // Javascript Program to print the    // Diagonals of a Matrix     let MAX = 100;          // Function to print the Principal Diagonal    function printPrincipalDiagonal(mat, n)    {      document.write("Principal Diagonal: ");       for (let i = 0; i < n; i++)      {        // Printing principal diagonal        document.write(mat[i][i] + ", ");      }      document.write("</br>");    }     // Function to print the Secondary Diagonal    function printSecondaryDiagonal(mat, n)    {      document.write("Secondary Diagonal: ");      let k = n - 1;       for (let i = 0; i < n; i++)      {        // Printing secondary diagonal        document.write(mat[i][k--] + ", ");      }      document.write("</br>");    }         let n = 4;    let a = [[1, 2, 3, 4],             [5, 6, 7, 8],             [1, 2, 3, 4],             [5, 6, 7, 8]];    printPrincipalDiagonal(a, n);    printSecondaryDiagonal(a, n);     </script>
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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Rajput-Ji
29AjayKumar
yashbeersingh42
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Code_Mech
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divyeshrabadiya07
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