# Print all the sub diagonal elements of the given square matrix

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

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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++ implementation of the approach ` `#include ` `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 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 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# 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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Improved By : jit_t, mohit kumar 29, Code_Mech

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