Java Program to Compute the Sum of Diagonals of a Matrix Last Updated : 21 May, 2025 Summarize Suggest changes Share Like Article Like Report For a given 2D square matrix of size N*N, our task is to find the sum of elements in the Principal and Secondary diagonals. For example, analyze the following 4 × 4 input matrix.m00 m01 m02 m03m10 m11 m12 m13m20 m21 m22 m23m30 m31 m32 m33Basic Input/Output:Input 1: 6 7 3 4 8 9 2 1 1 2 9 6 6 5 7 2Output 1: Principal Diagonal: 26 Secondary Diagonal: 14 Input 2: 2 2 2 1 1 1 3 3 3Output 2: Principal Diagonal: 6 Secondary Diagonal: 6Understanding Diagonals in a Square Matrix:The diagonal on which the row number and column number are the same (like elements in positions like (1,1), (2,2), (3,3), (4,4), and so on) is known as the principal diagonal or main diagonal of a square matrix.The diagonal in which the sum of the row number and column number is equal to one less than the size of the matrix is called the secondary diagonal. It runs from the top-right corner to the bottom-left corner of a square matrix.Naive Approach: Using Nested Loops to Identify DiagonalsWe are going to use nested loops to iterate over the elements in the matrix and going to check if it belongs to the principal or secondary diagonal based on the condition.Example: Below is the naive approach for finding the sum of diagonals of a matrix. Java // Java Program to Find the Sum of Diagonals of a Matrix // Importing input output classes import java.io.*; // Main Class public class Geeks { // To calculate Sum of Diagonals static void Sum_of_Diagonals1(int[][] matrix, int N) { // Declaring and initializing two variables to zero // initially for primary and secondary diagonal // count int Pd = 0, Sd = 0; // Two Nested for loops for iteration over a matrix // Outer loop for rows for (int k = 0; k < N; k++) { // Inner loop for columns for (int l = 0; l < N; l++) { // Condition for the principal // diagonal if (k == l) Pd += matrix[k][l]; // Condition for the secondary diagonal if ((k + l) == (N - 1)) Sd += matrix[k][l]; } } // Print and display the sum of primary diagonal System.out.println("Sum of Principal Diagonal:" + Pd); // Print and display the sum of secondary diagonal System.out.println("Sum of Secondary Diagonal:" + Sd); } // Main driver method static public void main(String[] args) { // Input integer array // Custom entries in an array int[][] b = { { 8, 2, 13, 4 }, { 9, 16, 17, 8 }, { 1, 22, 3, 14 }, { 15, 6, 17, 8 } }; // Passing the array as an argument to the // function defined above Sum_of_Diagonals1(b, 4); } } OutputSum of Principal Diagonal:35 Sum of Secondary Diagonal:58 Time complexity: O(N2)Auxiliary space: O(1)Let's now discuss the efficient approach in order to solve this problem.Optimized Approach: Access Diagonal Elements Directly by IndexThe idea to find the sum of values of principal diagonal is to iterate to N and use the value of matrix[row][row] for the summation of principal diagonal and to find the sum of values of secondary diagonal is to use the value of matrix[row][N - (row + 1)] for summation.Example: Below is the efficient approach for finding the sum of diagonals of a matrix. Java // Java Program to Find the Sum of Diagonals of a Matrix // Importing input output classes import java.io.*; // Main Class public class Geeks { // To calculate Sum of Diagonals static void Sum_of_Diagonals(int[][] matrix, int N) { // Declaring and initializing two variables to zero // initially for primary and secondary diagonal // count int Pd = 0, Sd = 0; for(int i=0; i<N; i++) { // Since for primary diagonal sum the value of // row and column are equal Pd += matrix[i][i]; // For secondary diagonal sum values of i'th index // and j'th index sum is equal to n-1 at each // stage of matrix Sd += matrix[i][N-(i+1)]; } // Print and display the sum of primary diagonal System.out.println("Sum of Principal Diagonal:" + Pd); // Print and display the sum of secondary diagonal System.out.println("Sum of Secondary Diagonal:" + Sd); } // Main driver method static public void main(String[] args) { // Input integer array // Custom entries in an array int[][] b = { { 8, 2, 13, 4 }, { 9, 16, 17, 8 }, { 1, 22, 3, 14 }, { 15, 6, 17, 8 } }; // Passing the array as an argument to the // function defined above Sum_of_Diagonals(b, 4); } } OutputSum of Principal Diagonal:35 Sum of Secondary Diagonal:58 Time complexity: O(N)Auxiliary space: O(1) Advertise with us Next Article Java Program to Interchange Elements of First and Last in a Matrix Across Rows K Kanchan_Ray Follow Similar Reads Java Programs - Java Programming Examples In this article, we will learn and prepare for Interviews using Java Programming Examples. 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Using Collections.reverseOrder()In this example, we will use Collections.reverseO 2 min read Java Program to Sort the Elements of an Array in Ascending OrderHere, we will sort the array in ascending order to arrange elements from smallest to largest, i.e., ascending order. So the easy solution is that we can use the Array.sort method. We can also sort the array using Bubble sort.1. Using Arrays.sort() MethodIn this example, we will use the Arrays.sort() 2 min read Remove duplicates from Sorted ArrayGiven a sorted array arr[] of size n, the goal is to rearrange the array so that all distinct elements appear at the beginning in sorted order. Additionally, return the length of this distinct sorted subarray.Note: The elements after the distinct ones can be in any order and hold any value, as they 7 min read Java Program to Merge Two ArraysIn Java, merging two arrays is a good programming question. We have given two arrays, and our task is to merge them, and after merging, we need to put the result back into another array. In this article, we are going to discuss different ways we can use to merge two arrays in Java.Let's now see the 5 min read Java Program to Check if two Arrays are Equal or notIn Java, comparing two arrays means checking if they have the same length and identical elements. This checking process ensures that both arrays are equivalent in terms of content and structure.Example:In Java, the simplest way to check if two arrays are equal in Java is by using the built-in Arrays 3 min read Remove all Occurrences of an Element from Array in JavaIn Java, removing all occurences of a given element from an array can be done using different approaches that are,Naive approach using array copyJava 8 StreamsUsing ArrayList.removeAll()Using List.removeIf()Problem Stament: Given an array and a key, the task is to remove all occurrences of the speci 5 min read Java Program to Find Common Elements Between Two ArraysGiven two arrays and our task is to find their common elements. Examples:Input: Array1 = ["Article", "for", "Geeks", "for", "Geeks"], Array2 = ["Article", "Geeks", "Geeks"]Output: [Article, Geeks]Input: Array1 = ["a", "b", "c", "d", "e", "f"], Array2 = ["b", "d", "e", "h", "g", "c"]Output: [b, c, d, 4 min read Array Copy in JavaIn Java, copying an array can be done in several ways, depending on our needs such as shallow copy or deep copy. In this article, we will learn different methods to copy arrays in Java.Example:Assigning one array to another is an incorrect approach to copying arrays. It only creates a reference to t 6 min read Java Program to Left Rotate the Elements of an ArrayIn Java, left rotation of an array involves shifting its elements to the left by a given number of positions, with the first elements moving around to the end. There are different ways to left rotate the elements of an array in Java.Example: We can use a temporary array to rotate the array left by " 5 min read Java 2-D Arrays (Matrix) ProgramsPrint a 2D Array or Matrix in JavaIn this article, we will learn to Print 2 Dimensional Matrix. 2D-Matrix or Array is a combination of Multiple 1 Dimensional Arrays. In this article we cover different methods to print 2D Array. When we print each element of the 2D array we have to iterate each element so the minimum time complexity 4 min read Java Program to Add two MatricesGiven two matrices A and B of the same size, the task is to add them in Java. Examples: Input: A[][] = {{1, 2}, {3, 4}} B[][] = {{1, 1}, {1, 1}} Output: {{2, 3}, {4, 5}} Input: A[][] = {{2, 4}, {3, 4}} B[][] = {{1, 2}, {1, 3}} Output: {{3, 6}, {4, 7}}Program to Add Two Matrices in JavaFollow the Ste 2 min read Sorting a 2D Array according to values in any given column in JavaWe are given a 2D array of order N X M and a column number K ( 1<=K<=m). Our task is to sort the 2D array according to values in Column K.Examples:Input: If our 2D array is given as (Order 4X4) 39 27 11 42 10 93 91 90 54 78 56 89 24 64 20 65Sorting it by values in column 3 Output: 39 27 11 422 3 min read Java Program to Check if two Arrays are Equal or notIn Java, comparing two arrays means checking if they have the same length and identical elements. This checking process ensures that both arrays are equivalent in terms of content and structure.Example:In Java, the simplest way to check if two arrays are equal in Java is by using the built-in Arrays 3 min read Java Program to Find Transpose of MatrixTranspose of a matrix is obtained by changing rows to columns and columns to rows. In other words, the transpose of A[ ][ ] is obtained by changing A[i][j] to A[j][i]. Example of First Transpose of MatrixInput: [ [ 1 , 2 , 3 ] , [ 4 , 5 , 6 ] , [ 7 , 8 , 9 ] ]Output: [ [ 1 , 4 , 7 ] , [ 2 , 5 , 8 ] 5 min read Java Program to Find the Determinant of a MatrixThe determinant of a matrix is a special calculated value that can only be calculated if the matrix has same number of rows and columns (square matrix). It is helpful in determining the system of linear equations, image processing, and determining whether the matrix is singular or non-singular.In th 5 min read Java Program to Find the Normal and Trace of a MatrixIn Java, when we work with matrices, there are two main concepts, and these concepts are Trace and Normal of a matrix. In this article, we will learn how to calculate them and discuss how to implement them in code. Before moving further, let's first understand what a matrix is. What is a Matrix?A ma 3 min read Java Program to Print Boundary Elements of the MatrixIn this article, we are going to learn how to print only the boundary elements of a given matrix in Java. Boundary elements mean the elements from the first row, last row, first column, and last column.Example:Input : 1 2 3 4 5 6 7 8 9Output: 1 2 3 4 6 7 8 9Now, let's understand the approach we are 3 min read Java Program to Rotate Matrix ElementsA matrix is simply a two-dimensional array. So, the goal is to deal with fixed indices at which elements are present and to perform operations on indexes such that elements on the addressed should be swapped in such a manner that it should look out as the matrix is rotated.For a given matrix, the ta 6 min read Java Program to Compute the Sum of Diagonals of a MatrixFor a given 2D square matrix of size N*N, our task is to find the sum of elements in the Principal and Secondary diagonals. For example, analyze the following 4 × 4 input matrix.m00 m01 m02 m03m10 m11 m12 m13m20 m21 m22 m23m30 m31 m32 m33Basic Input/Output:Input 1: 6 7 3 4 8 9 2 1 1 2 9 6 6 5 7 2Out 4 min read Java Program to Interchange Elements of First and Last in a Matrix Across RowsFor a given 4 × 4 matrix, the task is to interchange the elements of the first and last rows and then return the resultant matrix. Illustration: Input 1: 1 1 5 0 2 3 7 2 8 9 1 3 6 7 8 2 Output 1: 6 7 8 2 2 3 7 2 8 9 1 3 1 1 5 0 Input 2: 7 8 9 10 11 13 14 1 15 7 12 22 11 21 30 1 Output 2: 11 21 30 1 3 min read Java Program to Interchange Elements of First and Last in a Matrix Across ColumnsFor a given 4 x 4 matrix, the task is to interchange the elements of the first and last columns and then return the resultant matrix.Example Test Case for the ProblemInput : 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Output : 4 2 3 1 8 6 7 5 12 10 11 9 16 14 15 13 Implementation of Interchange Elements o 2 min read Java String ProgramsJava Program to Get a Character from a StringGiven a String str, the task is to get a specific character from that String at a specific index. Examples:Input: str = "Geeks", index = 2Output: eInput: str = "GeeksForGeeks", index = 5Output: F Below are various ways to do so: Using String.charAt() method: Get the string and the indexGet the speci 5 min read Replace a character at a specific index in a String in JavaIn Java, here we are given a string, the task is to replace a character at a specific index in this string. Examples of Replacing Characters in a StringInput: String = "Geeks Gor Geeks", index = 6, ch = 'F'Output: "Geeks For Geeks."Input: String = "Geeks", index = 0, ch = 'g'Output: "geeks"Methods t 3 min read Reverse a String in JavaIn Java, reversing a string means reordering the string characters from the last to the first position. Reversing a string is a common task in many Java applications and can be achieved using different approaches. In this article, we will discuss multiple approaches to reverse a string in Java with 7 min read Java Program to Reverse a String using StackThe Stack is a linear data structure that follows the LIFO(Last In First Out) principle, i.e, the element inserted at the last is the element to come out first. Approach: Push the character one by one into the Stack of datatype character.Pop the character one by one from the Stack until the stack be 2 min read Sort a String in Java (2 different ways)The string class doesn't have any method that directly sorts a string, but we can sort a string by applying other methods one after another. The string is a sequence of characters. In java, objects of String are immutable which means a constant and cannot be changed once created. Creating a String T 6 min read Swapping Pairs of Characters in a String in JavaGiven string str, the task is to write a Java program to swap the pairs of characters of a string. If the string contains an odd number of characters then the last character remains as it is. Examples: Input: str = “Javaâ€Output: aJav Explanation: The given string contains even number of characters. 3 min read Check if a given string is Pangram in JavaGiven string str, the task is to write Java Program check whether the given string is a pangram or not. A string is a pangram string if it contains all the character of the alphabets ignoring the case of the alphabets. Examples: Input: str = "Abcdefghijklmnopqrstuvwxyz"Output: YesExplanation: The gi 3 min read Print first letter of each word in a string using regexGiven a string, extract the first letter of each word in it. "Words" are defined as contiguous strings of alphabetic characters i.e. any upper or lower case characters a-z or A-Z. Examples: Input : Geeks for geeksOutput :Gfg Input : United KingdomOutput : UKBelow is the Regular expression to extract 3 min read Java Program to Determine the Unicode Code Point at Given Index in StringASCII is a code that converts the English alphabets to numerics as numeric can convert to the assembly language which our computer understands. For that, we have assigned a number against each character ranging from 0 to 127. Alphabets are case-sensitive lowercase and uppercase are treated different 5 min read Remove Leading Zeros From String in JavaGiven a string of digits, remove leading zeros from it.Illustrations: Input : 00000123569Output: 123569Input: 000012356090Output: 12356090Approach: We use the StringBuffer class as Strings are immutable.Count leading zeros by iterating string using charAt(i) and checking for 0 at the "i" th indices. 3 min read Compare two Strings in JavaString in Java are immutable sequences of characters. Comparing strings is the most common task in different scenarios such as input validation or searching algorithms. In this article, we will learn multiple ways to compare two strings in Java with simple examples.Example:To compare two strings in 4 min read Compare two strings lexicographically in JavaIn this article, we will discuss how we can compare two strings lexicographically in Java. One solution is to use Java compareTo() method. The method compareTo() is used for comparing two strings lexicographically in Java. Each character of both the strings is converted into a Unicode value for comp 3 min read Java program to print Even length words in a StringGiven a string s, write a Java program to print all words with even length in the given string. Example to print even length words in a String Input: s = "i am Geeks for Geeks and a Geek" Output: am GeekExample:Java// Java program to print // even length words in a string class GfG { public static v 3 min read Insert a String into another String in JavaGiven a String, the task is to insert another string in between the given String at a particular specified index in Java. Examples: Input: originalString = "GeeksGeeks", stringToBeInserted = "For", index = 4 Output: "GeeksForGeeks" Input: originalString = "Computer Portal", stringToBeInserted = "Sci 4 min read Split a String into a Number of Substrings in JavaGiven a String, the task it to split the String into a number of substrings. A String in java can be of 0 or more characters. Examples : (a) "" is a String in java with 0 character (b) "d" is a String in java with 1 character (c) "This is a sentence." is a string with 19 characters. Substring: A Str 5 min read Article Tags : Java Java-Array-Programs Practice Tags : Java Like