Java Program to check if matrix is upper triangular

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

Examples: 

Input : mat[4][4] = {{1, 3, 5, 3},
                     {0, 4, 6, 2},
                     {0, 0, 2, 5},
                     {0, 0, 0, 6}};
Output : Matrix is in Upper Triangular form.

Input : mat[4][4] = {{5, 6, 3, 6},
                     {0, 4, 6, 6},
                     {1, 0, 8, 5},
                     {0, 1, 0, 6}};
Output : Matrix is not in Upper Triangular form.

Java

// Java Program to check upper
// triangular matrix.
import java.util.*;
import java.lang.*;

public class GfG
{
    private static final int N = 4;

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

    // driver function
    public static void main(String argc[]){
        int[][] mat= { { 1, 3, 5, 3 },
                       { 0, 4, 6, 2 },
                       { 0, 0, 2, 5 },
                       { 0, 0, 0, 6 } };

        if (isUpperTriangularMatrix(mat))
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}

/* This code is contributed by Sagar Shukla */

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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