Upper Triangular Matrix is a matrix in which all the elements below the principal matrix are 0. A necessary condition is that matrix must be Square matrix in nature. If the matrix is not a square matrix, it can never be called the upper triangular matrix.
Examples
Input 1: mat[][] = { {2, 1, 4},
{1, 2, 3},
{3, 6, 2} }
Output : mat[][]= { {2, 1, 4},
{0, 2, 3},
{0, 0, 2} }
Explanation: All the element below the principal diagonal needs to be 0.
Input 2 : mat[][]= { {4,7},
{2,8} }
Output : mat[][]= { {4,7},
{0,8} }
Input 3 : mat[][]= { {2,1,4,6},
{1,2,3,7},
{3,6,2,8} }
Output : Matrix should be a Square Matrix
 Approach:
- If the matrix has equal rows and columns, continue the program else exit the program.
- Run the loop over the whole matrix, and for the rows whose row number is greater than column number, make the element at that position equal to 0.
Below is the implementation of the above approach:
Java
// Java Program to print the upper triangular matriximport java.io.*;Â
class GFG {       // Print matrix using iterative approach    public static void printMatrix(int[][] a)    {        for (int i = 0; i < a.length; i++) {            for (int j = 0; j < a[0].length; j++)                System.out.print(a[i][j] + " ");            System.out.println();        }    }    public static void upperTriangularMatrix(int matrix[][])    {        int row = matrix.length;        int col = matrix[0].length;               // if number of rows and        // columns are not equal,then        // return back        if (row != col) {            System.out.println(                "Matrix should be a Square Matrix");            return;        }        else {                       // looping over the whole matrix            for (int i = 0; i < row; i++) {                for (int j = 0; j < col; j++) {                                       // for the rows ,whose row number is                    // greater then column number,mark the                    // element as 0                    if (i > j) {                        matrix[i][j] = 0;                    }                }            }Â
            System.out.println(                "Upper Triangular Matrix is given by :-");                       // printing the upper triangular matrix            printMatrix(matrix);        }    }    public static void main(String[] args)    {        int mat[][] = { { 2, 1, 4 }, { 1, 2, 3 }, { 3, 6, 2 } };               // calling the function        upperTriangularMatrix(mat);    }} |
Output
Upper Triangular Matrix is given by :- 2 1 4 0 2 3 0 0 2
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 Space Complexity: 0(N^2)
Time Complexity: 0(N^2)
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