This is the Java Program to Display Upper/Lower Triangle of a Matrix.

Given a square matrix, print it’s upper and lower triangle.

Example:

Matrix:

0 0 1 1

0 1 1 1

0 0 0 1

0 0 0 0

Output:

Upper Triangle

0 0 1 1

0 1 1

0 0

0

Lower Triangle

1

0 1

0 0 0

Traverse through the matrix. To display the upper triangle **check whether the sum of i and j indexes is less than the order of the matrix** if it is then print the element matrix[i][j]. Similarly, to display the lower triangle **check whether the sum of i and j indexes is greater than or equal to the order of the matrix** if it is then print the element matrix[i][j].

Here is the source code of the Java Program to Display Upper/Lower Triangle of a Matrix. The program is successfully compiled and tested using IDE IntelliJ Idea in Windows 7. The program output is also shown below.

`//Java Program to Display Upper/Lower Triangle of a Matrix`

import java.io.BufferedReader;

import java.io.InputStreamReader;

public class UpperAndLowerTriangle {

`// Function to display upper and lower triangle`

static void displayUpperAndLowerTriangle(int[][] matrix){

int order = matrix.length;

int i,j;

for(i=0; i<order; i++){

for(j=0; j<order;j++){

if((i+j) <order)

System.out.print(matrix[i][j] + "\t");

`}`

System.out.println();

`}`

for(i=0; i<order; i++){

for(j=0; j<order;j++){

if((i+j) >=order)

System.out.print(matrix[i][j] + "\t");

`}`

System.out.println();

`}`

`}`

`// Function to read user input`

public static void main(String[] args) {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

int order;

System.out.println("Enter the order of the matrix");

try{

order = Integer.parseInt(br.readLine());

`}`

catch(Exception e){

System.out.println("An error occurred");

return;

`}`

int[][] matrix = new int[order][order];

System.out.println("Enter matrix elements");

int i,j;

for(i=0; i<order; i++){

for(j=0; j<order; j++){

try{

matrix[i][j] = Integer.parseInt(br.readLine());

`}`

catch(Exception e){

System.out.println("An error occurred");

return;

`}`

`}`

`}`

System.out.println("Tha matrix is");

for(i=0; i<order; i++){

for(j=0; j<order; j++){

System.out.print(matrix[i][j] + "\t");

`}`

System.out.println();

`}`

System.out.println("The upper and lower triangle is");

displayUpperAndLowerTriangle(matrix);

`}`

`}`

1. In function displayUpperAndLowerTriangle(), the order variable is initialized to matrix.length, which is the order of the matrix passed.

2. Within the first set of nested loops, the condition if((i+j) < order) is checked to display the upper triangle of the matrix.

3. Within the second set of nested loops, the condition if((i+j) >= order) is checked to display the lower triangle of the matrix.

**Time Complexity: O(nm)** where n is the number of rows and m is the number of columns in the matrix respectively.

Case 1 (Simple Test Case): Enter the order of the matrix 4 Enter matrix elements 0 0 1 1 0 1 1 1 0 0 0 1 0 0 0 0 The matrix is 0 0 1 1 0 1 1 1 0 0 0 1 0 0 0 0 The upper and lower triangle is 0 0 1 1 0 1 1 0 0 0 1 0 1 0 0 0 Case 2 (Simple Test Case - another example): Enter the order of the matrix 3 Enter matrix elements 1 2 3 4 5 6 7 8 9 The matrix is 1 2 3 4 5 6 7 8 9 The upper and lower triangle is 1 2 3 4 5 7 6 8 9

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