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Print all the sub diagonal elements of the given square matrix
  • Last Updated : 21 Jun, 2019

Given a square matrix mat[][] of size n * n. The task is to print all the elements which lie on the sub-diagonal of the given matrix.

Examples:

Input: mat[][] = {
{1, 2, 3},
{3, 3, 4, },
{2, 4, 6}}
Output: 3 4

Input: mat[][] = {
{1, 2, 3, 4},
{3, 3, 4, 4},
{2, 4, 6, 3},
{1, 1, 1, 3}}
Output: 3 4 1

Approach: The sub-diagonal of a square matrix is the set of elements that lie directly below the elements comprising the main diagonal. As for main diagonal elements, their indexes are like (i = j), for sub-diagonal elements their indexes are as i = j + 1 (i denotes row and j denotes column).



Hence elements arr[1][0], arr[2][1], arr[3][2], arr[4][3], …. are the elements of sub-diagonal.

Either traverse all elements of matrix and print only those where i = j + 1 which requires O(n2) time complexity or print traverse only row from 1 to rowCount – 1 and print elements as arr[row][row – 1].

Below is the implementation of the above approach:

C++




// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
#define R 4
#define C 4
  
// Function to print the sub diagonal
// elements of the given matrix
void printSubDiagonal(int arr[R][C])
{
    for (int i = 1; i < R; i++) {
        cout << arr[i][i - 1] << " ";
    }
}
  
// Driver code
int main()
{
    int arr[R][C] = { { 1, 2, 3, 4 },
                      { 5, 6, 7, 8 },
                      { 9, 10, 11, 12 },
                      { 13, 14, 15, 16 } };
  
    printSubDiagonal(arr);
  
    return 0;
}

Java




// Java implementation of the approach
import java.io.*;
  
class GFG
{
      
static int R = 4;
static int C = 4;
  
// Function to print the sub diagonal
// elements of the given matrix
static void printSubDiagonal(int arr[][])
{
    for (int i = 1; i < R; i++)
    {
            System.out.print(arr[i][i - 1] + " ");
    }
}
  
// Driver code
public static void main (String[] args)
{
  
    int arr[][] = { { 1, 2, 3, 4 },
                    { 5, 6, 7, 8 },
                    { 9, 10, 11, 12 },
                    { 13, 14, 15, 16 } };
  
    printSubDiagonal(arr);
  
}
}
  
// This code is contributed by ajit.

Python3




# Python3 implementation of the approach
R = 4
C = 4
  
# Function to print the sub diagonal
# elements of the given matrix
def printSubDiagonal(arr):
  
    for i in range(1, R):
        print(arr[i][i - 1], end = " ")
  
# Driver code
arr = [[ 1, 2, 3, 4 ],
       [ 5, 6, 7, 8 ],
       [ 9, 10, 11, 12 ],
       [ 13, 14, 15, 16 ]]
  
printSubDiagonal(arr);
  
# This code is contributed
# by Mohit Kumar

C#




// C# implementation of the approach
using System;
class GFG
{
    static int R = 4;
    static int C = 4;
      
    // Function to print the sub diagonal
    // elements of the given matrix
    static void printSubDiagonal(int[,] arr)
    {
        for (int i = 1; i < R; i++)
        {
                Console.Write(arr[i, i - 1] + " ");
        }
    }
      
    // Driver code
    public static void Main ()
    {
        int [,]arr = {{ 1, 2, 3, 4 },
                      { 5, 6, 7, 8 },
                      { 9, 10, 11, 12 },
                      { 13, 14, 15, 16 }};
      
        printSubDiagonal(arr);
    }
}
  
// This code is contributed by CodeMech.
Output:
5 10 15

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