Question

8. Ann x n matrix that is filled with the numbers 1,2,3, ....n2 is a magic square if the sum of the elements in each row, in each column, and in the two main diagonals is the same value. For example, 16 3 213 5 10 11 8 9 6 7 12 4 15 14 1 Write the program that reads in 16 values from the keyboard and tests whether they form a magic square when put into a 4 x 4 array. Place the numbers in the matrix from top to bottonm left to right (i.e. the first number goes in the top left position and the last goes in the bottom right position)

Answer 1

8. Given Below is the java program for the checking 4 by 4 matrix is a magic square or not :

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import java.util.*;
import java.lang.*;
import java.io.*;

public class test {
    public static void main (String[] args) {
        Scanner in = new Scanner(System.in);     //creating input reader
        PrintWriter w = new PrintWriter(System.out);     //creating writer

        int[][] mat = new int[4][4];                     //declare the 4 by 4 input matrix

        for (int i = 0; i < 4; i++) {                   //taking input for matrix
            for (int j = 0; j < 4; j++) {
                mat[i][j] = in.nextInt();
            }
        }
        HashSet<Integer> sumValues = new HashSet<>(); //create a hashset to store all calculated sum

        for (int i = 0; i < 4; i++) {                   //taking input for matrix

            int rowSum = 0, columnSum = 0;              // variables to calculate row and column sum repectively
            for (int j = 0; j < 4; j++) {
                rowSum += mat[i][j];                    // calculating row sum
                columnSum += mat[j][i];                 //calculating column sum
            }

            // adding row and column values to hashset
            sumValues.add(rowSum);
            sumValues.add(columnSum);
        }

        int leftDiagonalsum = mat[0][0] + mat[1][1] + mat[2][2] + mat[3][3];    //calculating left diagonam sum
        int rightDiagonalsum = mat[0][3] + mat[1][2] + mat[2][1] + mat[3][0];   //calculating right diagonam sum

        //adding diagonal sum to hashset
        sumValues.add(leftDiagonalsum);
        sumValues.add(rightDiagonalsum);

        //if all sum values are same the hashset should contain only single value
        if (sumValues.size() == 1) {
            w.println("Yes, Its a magic square");
        }

        //otherwise atleast 2 sumvalues are different
        else {
            w.println("No, Its not a magic square");
        }

        w.close();
    }

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=> Find the output and compilation/running screenshot below

java>javac test.java :java>java test 16 3 2 13 5 10 11 8 96 7 12 4 15 14 1 es, Its a magic square C: java>

7. The the required method below :

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    public static Boolean sameSet(int[] a, int[] b) {
        HashSet<Integer> hsa = new HashSet<>(), hsb = new HashSet<>(); //creating HashSet for both arrays
        for (int x : a)                                                //filling hashSet for array a
            hsa.add(x);

        for (int x : b)                                                //filling hashSet for array b
            hsb.add(x);

        return hsa.equals(hsb);                                        // check if 2 hashsets are equal
    }

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For running and compiling of the program ,find the screenshot below :

Command Prompt :java>javac test.java :java> java test 1 2 345 6 1 2 345 1 true java>java test 1 234 5 1 234 6 false :java>