C++ Program to check if matrix is lower triangular

Given a square matrix and the task is to check the matrix is in lower triangular form or not. A square matrix is called lower triangular if all the entries above the main diagonal are zero. 

Examples: 

Input : mat[4][4] = {{1, 0, 0, 0},
                     {1, 4, 0, 0},
                     {4, 6, 2, 0},
                     {0, 4, 7, 6}};
Output : Matrix is in lower triangular form.

Input : mat[4][4] = {{1, 0, 0, 0},
                     {4, 3, 0, 1},
                     {7, 9, 2, 0},
                     {8, 5, 3, 6}};
Output : Matrix is not in lower triangular form.

C++

// Program to check lower
// triangular matrix.
#include <bits/stdc++.h>
#define N 4
using namespace std;

// Function to check matrix is in
// lower triangular form or not.
bool isLowerTriangularMatrix(int mat[N][N])
{
    for (int i = 0; i < N; i++)
        for (int j = i + 1; j < N; j++)
            if (mat[i][j] != 0)
                return false;
    return true;
}

// Driver function.
int main()
{
    int mat[N][N] = { { 1, 0, 0, 0 },
                      { 1, 4, 0, 0 },
                      { 4, 6, 2, 0 },
                      { 0, 4, 7, 6 } };

    // Function call
    if (isLowerTriangularMatrix(mat))
        cout << "Yes";
    else
        cout << "No";
    return 0;
}

Output: 

Yes

Time Complexity: O(n²), where n represents the number of rows and columns of the matrix.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Program to check if matrix is lower triangular for more details!

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