Java 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.

Java

// Java Program to check for
// a lower triangular matrix.
import java.io.*;

class Lower_triangular
{
    int N = 4;

    // Function to check matrix is
    // in lower triangular form or not.
    boolean isLowerTriangularMatrix(int mat[][])
    {
        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.
    public static void main(String args[])
    {
        Lower_triangular ob = new Lower_triangular();
        int mat[][] = { { 1, 0, 0, 0 },
                        { 1, 4, 0, 0 },
                        { 4, 6, 2, 0 },
                        { 0, 4, 7, 6 } };

        // Function call
        if (ob.isLowerTriangularMatrix(mat))
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}

// This code is contributed by Anshika Goyal.

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.

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