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Merging two 2D arrays (M + N)

I am a first year programming trying to solve this challenge that was given to us students at uni.
Question image
There's a typo at where it says (N + K) whereas in fact it's actually (M+K) columns.
My attempt for this question goes as follows
public static int[][] mergeArrays(int[][] arrayA, int[][] arrayB){
int rows = 3;
int columns = arrayA[0].length + arrayB[0].length;
int[][] mergedArray = new int[rows][columns];
int k = 0;
for (int i = 0; i < rows; i++)
{
for ( int j = 0 ; j < columns; j++)
{
try
{
mergedArray[i][j] = arrayA[i][j];
}
catch (ArrayIndexOutOfBoundsException e)
{
mergedArray[i][j] = arrayB[i][k];
k += 1;
}
}
}
return mergedArray;
}
public static void main(String [] args)
{
int [][] a1 = { {1,2,3,3,3} , {3,2,1,6,3} , {4,5,6,1,3} };
int [][] a2 = { {1,9,7,2,3} , {0,7,8,3,2} , {3,8,9,7,2} };
int[][] m = mergeArrays(a1,a2);
for (int[] x : m)
{
for (int y : x)
{
System.out.print(y + " ");
}
System.out.println();
}
}
The program doesn't work for some reason. I don't know what's wrong with my approach here. Would really appreciate if someone helps me out.

Without using any libraries, in a manual way, here is my working answer.
I didn't use any of them, since we were not allowed, when I was a student.
public class Main {
private static int[][] mergeArrays(int[][] a1, int[][] a2) {
// Count rows and cols length.
int rows = a1.length;
int cols_a1 = a1[0].length;
int cols_a2 = a2[0].length;
// Total number of cols
int cols = cols_a2 + cols_a1;
int [][] merged = new int[rows][cols];
for (int i = 0; i < rows ; ++i) {
for (int j = 0; j < cols_a1; ++j) {
merged[i][j] = a1[i][j];
}
// To not overwrite values,
// the trick is to add an offset, while assigning,
// which is the amount of elements (cols_a1) used by the previous loop.
// Basically, we are shifting the k-index by this constant,
// as to not overwrite the values assigned from the previous
// inner loop.
for (int k = 0; k < cols_a2; ++k) {
merged[i][cols_a1 + k] = a2[i][k];
}
}
// Return the merged array
return merged;
}
// I refactored your good printing code into a method, for readability.
private static void print2darray(int[][] array2d) {
for (int[] x : array2d) {
for (int y : x) {
System.out.print(y + " ");
}
System.out.println();
}
}
public static void main(String[] args) {
int [][] a1 = {{1,2,3,3,3} , {3,2,1,6,3} , {4,5,6,1,3}};
int [][] a2 = {{1,9,7,2,3} , {0,7,8,3,2} , {3,8,9,7,2}};
int [][] merged = mergeArrays(a1, a2);
print2darray(merged);
}
}
The result is the same, as expected, from your question image:
1 2 3 3 3 1 9 7 2 3
3 2 1 6 3 0 7 8 3 2
4 5 6 1 3 3 8 9 7 2

Since you're a student I think to better if we give a hint, but since the solution is already there you can check this one as well:
public static int[] merge(int[] first,int[] second) {
return ArrayUtils.addAll(first, second);
}
public static void main(String[] args) {
int [][] a1 = { {1,2,3,3,3} , {3,2,1,6,3} , {4,5,6,1,3}};
int [][] a2 = { {1,9,7,2,3} , {0,7,8,3,2} , {3,8,9,7,2}};
int [][] a3 = new int[a1.length][];
for (int i = 0; i < a1.length; i++) {
a3[i] = merge(a1[i],a2[i]);
}
for (int[] ints : a3) {
StringJoiner joiner = new StringJoiner(",","[","]");
for (int i1 : ints) {
joiner.add(i1+"");
}
System.out.println(joiner.toString());
}
}

You are not merging it properly. Your logic is that if arrayA column index is out of bounds, you are adding from arrayB's columns. But what if that is also out of bounds, as in your case. Since you are always incrementing its index k. You could simply iterate over 2 arrays separately and merge into resulting array.
public static int[][] mergeArrays(int[][] arrayA, int[][] arrayB) {
int rows = 3;
int columns = arrayA[0].length + arrayB[0].length;
int[][] mergedArray = new int[rows][columns];
int k = 0;
for (int i = 0; i < rows; i++) {
for (int j = 0; j < arrayA[0].length; j++) {
mergedArray[i][k++] = arrayA[i][j];
}
for (int j = 0; j < arrayB[0].length; j++) {
mergedArray[i][k++] = arrayB[i][j];
}
k=0;
}
return mergedArray;
}

Printing the sum of rows and columns of 2 arrays

I am absolutely stuck. Any help would be appreciated. The question asks
1.Create two 2-dim arrays/matrices (random numbers, range 1 -500, where 1 and 500 should be declared as class constants). Both have the same dimensions.
2.Print the arrays.
3.Call a method to sum the 2 matrices. The sum of 2 matrices matrix_1 and matrix_2 is a matrix result, where for every row r and column c,
result_rc= matrix_1_rc+ matrix_2_rc
4.Print the resulting matrix.
I am stuck on 3 and 4. Part of the problem is I do not get the logic of what 3 is asking. Do I get the sum of each row and each column and add that to the second arrays sum of rows and columns. The second problem is I am absolutely lost on what to do next.
I have been researching for hours and trying different things.
import java.util.*;
public class Lab12p2 {
public static final int MAX = 500;
public static final int MIN = 1;
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.println("Enter the number of times to run the program");
int start = scan.nextInt();
while (start < 0) {
System.out.println("Error! Should be positive. REENTER");
start = scan.nextInt();
}
// end number of times validation
while (start > 0)// counter loop for how many times to run program {
System.out.println("Enter the size of the 2 arrays");
int SIZE = scan.nextInt();
while (SIZE < 0) {
System.out.println("Error! Should be positive. REENTER");
SIZE = scan.nextInt();
} // size validation
// start of methods
int[][] a = new int[SIZE][SIZE];
int[][] b = new int[SIZE][SIZE];// second array
System.out.println("The first array is ");
System.out.println();
randArray(a, SIZE, SIZE, MIN, MAX);
System.out.println("The second array is ");
System.out.println();
randArray(b, SIZE, SIZE, MIN, MAX);
sum2arrays(a, b, SIZE, SIZE);
start--;
}
public static void randArray(int[][] matrix, int row, int col, int low, int up) {
Random rand = new Random();
for (int r = 0; r < row; r++) {
for (int c = 0; c < col; c++) {
int random = matrix[r][c] = rand.nextInt(up - low + 1) + low;
System.out.print("\t" + random);
}
System.out.println();
}
}
public static void sum2arrays(int[][] matrix1, int[][] matrix2, int col, int row) {
int sumrow;
int sumtotalrow = 0;
for (int r = 0; r < matrix1.length; r++) {
sumrow = 0;
for (int c = 0; c < matrix1[r].length; c++) {
sumrow = sumrow + matrix1[r][c];
}
sumtotalrow = sumtotalrow + sumrow;
}
// testing
System.out.println("The sum of ALL the elements/row = " + sumtotalrow);
}
}
It should
Call a method to sum the 2 matrices. The sum of 2 matrices matrix_1 and matrix_2 is a matrix result, where for every row r and column c,
result_rc= matrix_1_rc+ matrix_2_rc (I dont know what that means) and then print the resulting matrix

public static void sum2arrays(int[][] matrix1, int[][]matrix2,int col,int row)
{
int sumrow;
ArrayList <Integer> three=new ArrayList<Integer>();
for (int r = 0; r < matrix1.length; r++)
{
sumrow = 0;
for (int c = 0; c < matrix1[r].length; c++)
{
three.add( matrix2[r][c] + matrix1[r][c]);
}
}
System.out.println("The matrix result is ");
System.out.println(three);
}

How to display methods in the console that read from a file?

I need to be able to display the Average, ColumnTotal, Highest/Lowest in row, RowTotal. I'm not sure whether it depends on something I did in the methods themselves that has to be changed, or if I can simply that call them with the correct arguments to read from a file. The text file that it reads from basically just inputs two integers that are separated by a space on the same line, those are the arguments I would like to be able to input. I'm not entirely sure how to do this. This is just an assignment from a College text book basically amped up by my Instructor called "TwoDimArray" which I've been able to find many examples of online but none of them had the 'read from file' portion that I have to do here, they all just used a normal array input such as "int[][] array = {{22, 37, 48, 68}} for the main method. I'm going to include the entire program in order to show exactly what I need to be displayed via println. I've been thinking about how to do this for quite a few hours now and decided that I definitely need help. Any help would be greatly appreciated! Thanks ahead of time.
import javax.swing.*;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class TwoDimArray {
private int arr[][];
public TwoDimArray() {
loadArray();
}
public void loadArray(){
/**
* loadArray() method loads user defined filename
* #return text file's contents
*/
String fileName = "";
try {
fileName = JOptionPane.showInputDialog("Enter file name: ");
}
catch (Exception e){
JOptionPane.showMessageDialog(null, "can not open " + fileName + " to read");
return;
}
try {
Scanner in = new Scanner(new File(fileName));
int rows, cols;
rows = in.nextInt();
cols = in.nextInt();
arr = new int[rows][cols];
for(int i = 0; i < rows; ++i){
for(int j = 0; j < cols; ++j){
arr[i][j] = in.nextInt();
}
}
in.close();
} catch (FileNotFoundException e) {
JOptionPane.showMessageDialog(null, "can not open " + fileName + " to read");
}
}
public int getArrayMaxValue(){
/**
* #return the max vale of the array
*/
int maxVal = Integer.MIN_VALUE;
for(int i = 0; i < arr.length; ++i){
for(int j = 0; j < arr.length; ++j){
if(arr[i][j] > maxVal){
maxVal = arr[i][j];
}
}
}
return maxVal;
}
public int getArrayMinValue(){
/**
* #return the minimum value of the array
*/
int minVal = Integer.MAX_VALUE;
for(int i = 0; i < arr.length; ++i){
for(int j = 0; j < arr.length; ++j){
if(arr[i][j] < minVal){
minVal = arr[i][j];
}
}
}
return minVal;
}
public static int getTotal(int[][] array) {
int total = 0;
for (int row = 0; row < array.length; row++) {
for (int col = 0; col < array[row].length; col++) {
total += array[row][col];
}
}
return total;
}
public static int getAverage(int[][] array) {
return getTotal(array) / getElementCount(array);
}
public static int getRowTotal(int[][] array, int row) {
int total = 0;
for (int col = 0; col < array[row].length; col++) {
total += array[row][col];
}
return total;
}
public static int getColumnTotal(int[][] array, int col) {
int total = 0;
for (int row = 0; row < array.length; row++) {
total += array[row][col];
}
return total;
}
public static int getHighestInRow(int[][] array, int row) {
int highest = array[row][0];
for (int col = 1; col < array[row].length; col++) {
if (array[row][col] > highest) {
highest = array[row][col];
}
}
return highest;
}
public static int getLowestInRow(int[][] array, int row) {
int lowest = array[row][0];
for (int col = 1; col < array[row].length; col++) {
if (array[row][col] < lowest) {
lowest = array[row][col];
}
}
return lowest;
}
public static int getElementCount(int[][] array) {
int count = 0;
for (int row = 0; row < array.length; row++) {
count += array[row].length;
}
return count;
}
public static void main(String[] args){
/**
* what to put in int[][] array to allow println of average, getrowtotal,
* etc..
*/
int[][] array = ???;
TwoDimArray twoDimArray = new TwoDimArray();
System.out.println("Max value: " + twoDimArray.getArrayMaxValue());
System.out.println("Min value: " + twoDimArray.getArrayMinValue());
System.out.println(getAverage(array));
}
}

0) Create numbers.txt in the root of your project. This is the file you will load array from. Example content as follows (2 rows, 3 columns):
2 3
1 2 3
4 5 6
1) You don't need your explicitly created int[][] array = ??? because there is already existing private int arr[][] which will be automatically loaded from file after you type it's name as intended in TwoDimArray constructor.
2) Since main method located at the same class as private int arr[][], you can access this private array without public getter/setter, and get average value like this:
// you don't need following line at all
// int[][] array = ???;
TwoDimArray twoDimArray = new TwoDimArray();
System.out.println("Max value: " + twoDimArray.getArrayMaxValue()); // Max value: 5
System.out.println("Min value: " + twoDimArray.getArrayMinValue()); // Min value: 1
// Average value
System.out.println(getAverage(twoDimArray.arr)); // 3, because 21 / 6 = 3
3) You probably got confused because getArrayMaxValue is signed as public int, and got invoked as twoDimArray.getArrayMaxValue(), whereas getAverage is public static int and must be called in different way.
I suggest marking getAverage as public int instead of public static int, and use private int arr[][] instead of int[][] array provided from arguments, so you will be able to call it the same way you do with other methods:
// Somewhere up
public int getAverage() {
return getTotal(arr) / getElementCount(arr);
}
// In your main method
System.out.println(twoDimArray.getAverage());

Basically, what you have there is a jagged array, it is not a bidimensional array. I will explain you the idea, you do the rest. That it is not a bidimensional array. This is an array of array, in each position you are pointing to a new array of int. If you never instantiated a new array on each position, then you have a position with a null value.
So going back with your question, you should read the entire line with the two integers that are on the same line. Be sure that the line in your file has in the first line 2 numbers separated by a space.
Then use the next() method to get the complete string
String line = in.next();
String[] parts = line.split(" ");
int val1 = Integer.parseInt(parts[0]);
int val2 = Integer.parseInt(parts[1]);
For this question:
what to put in int[][] array to allow println of average, getrowtotal,
int[][] array = new int[4];
array[0] = new int[] {10,20,30,40,50};
array[1] = new int[] {60,71,80,90,91};
array[2] = new int[] {1};
Hope this helps
Now, what do you think you have in array[3]? The answer is: NULL

you already read the array from file in your method loadArray...
Use it instead of trying to load the same thing again, remove static modifier from all method and use field arr instead of parameter array
private int getTotal() {
int total = 0;
for (int row = 0; row < arr.length; row++) {
for (int col = 0; col < arr[row].length; col++) {
total += arr[row][col];
}
}
return total;
}
private int getAverage() {
return getTotal() / getElementCount();
}
private int getElementCount() {
int count = 0;
for (int row = 0; row < arr.length; row++) {
count += arr[row].length;
}
return count;
}
public static void main(String[] args) {
TwoDimArray twoDimArray = new TwoDimArray();
System.out.println("Max value: " + twoDimArray.getArrayMaxValue());
System.out.println("Min value: " + twoDimArray.getArrayMinValue());
System.out.println(twoDimArray.getAverage());
}

Error when trying to print a transposed 2d array

While writing my code I'm getting stuck on I'm trying to return the new transposed array and actually transposing the array itself. I get the error cannot convert int to int[][]. i thought trans would be an array var. the problem code is at the way bottom. any help is greatly appreciated.
package workfiles;
import java.util.*;
import java.util.Scanner;
public class hw2 {
// Do not modify this method
public static void main(String[] args) {
try
{
int [][] iArray = enter2DPosArray();
System.out.println("The original array values:");
print2DIArray(iArray);
int [][] tArray = transposition(iArray);
System.out.println("The transposed array values:");
print2DIArray(tArray);
}
catch (InputMismatchException exception)
{
System.out.println("The array entry failed. The program will now halt.");
}
}
// A function that prints a 2D integer array to standard output
// It prints each row on one line with newlines between rows
public static void print2DIArray(int[][] output) {
for (int row = 0; row < output.length; row++) {
for (int column = 0; column < output[row].length; column++) {
System.out.print(output[row][column] + " ");
}
System.out.println();
}
}
// A function that enters a 2D integer array from the user
// It raises an InputMismatchException if the user enters anything other
// than positive (> 0) values for the number of rows, the number of
// columns, or any array entry
public static int[][] enter2DPosArray() throws InputMismatchException {
int row=0;
int col=0;
int arow=0;
int acol=0;
int holder;
Scanner numScan = new Scanner(System.in);
while (row<=0){
System.out.print("How many rows (>0) should the array have? ");
row = numScan.nextInt();
}
while (col<=0){
System.out.print("How many columns (>0) should the array have? ");
col = numScan.nextInt();
}
int[][] iArray = new int[row][col];
while (arow < row) {
while (acol < col) {
System.out.println("Enter a positive (> 0) integer value: ");
holder = numScan.nextInt();
iArray[arow][acol] = holder;
acol++;
}
if (acol >= col) {
acol = 0;
arow ++;
}
}
//arrayName[i][j]
numScan.close();
return iArray;
}
//!!! problem code here!!!
public static int[][] transposition(int [][] iArray) {
int m = iArray.length;
int n = iArray[0].length;
int trans[][];
for(int y = 0; y<m; y++){
for(int x = 0; x<n; x++){
trans = iArray[y][x] ;
}
}
return trans;
}
}

You missed two things
1.) initialization of trans
int trans[][]= new int [n][m];
2.) trans is a 2D array
trans[y][x] = iArray[y][x] ;
//trans = iArray[y][x] ; error
Update : To form this logic , we need index mapping like this
// trans iArray
// assign values column-wise row-wise
// trans[0][0] <= iArray[0][0]
// trans[1][0] <= iArray[0][1]
// trans[2][0] <= iArray[0][2]
mean traverse the iArrays row-wise and assign values to trans array columns-wise
int m = iArray.length;
int n = iArray[0].length;
// iArray[2][3]
int trans[][] = new int[n][m];
// 3 2
for(int y = 0; y<m; y++){
for(int x = 0; x<n; x++){
trans[x][y] = iArray[y][x] ;
}
}

Merge sort 3 way java

I have to make a 3 way merge sort of an array. the array length is a in a power of 3, i.e. 3,9,27 etc. So I can use only one split function and not "left","mid","right".
Would like to get an answer how to repair it and why does not it work.
I have written the code, however don't know how to get it to work.
Here it is:
EDITED THE CODE, STILL DOES NOT WORK
public class Ex3 {
public static void main(String[] args) { //main function
Scanner in = new Scanner(System.in); //scanner
int size = in.nextInt();
int[] arr = new int[size];
for (int i = 0; i<arr.length; i++){
arr[i] = in.nextInt();
}
in.close();
arr = merge3sort (arr); //send to the function to merge
for (int i = 0; i<arr.length; i++){ //printer
System.out.print(arr[i]+ " ");
}
}
static int[] split(int[] m, int thirdNum) { //split function that splits to 3 arrays
int third[] = new int[m.length/3];
int third1[]=new int[m.length/3];
int third2[]=new int[m.length/3];
for(int i = 0; i<=m.length/3; i++)
third[i]=m[i];
for(int i=0; i<=m.length/3;i++)
third1[i]=m[i+thirdNum];
for(int i=0; i<=m.length/3;i++)
third2[i]=m[i+2*thirdNum];
return merge(third,third1,third2);
//return null;
}
static int minOf3(int[] a3) { //function that finds out how what is the index of the smallest number
int num0 = a3[0];
int num1 = a3[1];
int num2 = a3[2];
int idx = 0;
if(num0<num1 && num1<num2)
idx=0;
if(num1<num0 && num0<num2)
idx=1;
else
idx=2;
return idx;
}
static int[] merge(int[] th0, int[] th1, int[] th2) { //function that sorts the numbers between 3 arrays
int len0=th0.length;
int len1=th1.length;
int len2=th2.length;
int[] united = new int[len0+len1+len2];
int ind = 0; int i0=0; int i1=0; int i2=0;
while(i0<len0 && i1<len1 && i2<len2){
if(th0[i0]<th1[i1]){
if(th0[i0]<th2[i2]){
united[ind]=th0[i0];
i0=i0+1;
}//end inner if
else{
united[ind]=th2[i2];
i2=i2+1;
}//end inner else
}//end outer if
else{
united[ind]=th1[i1];
i1=i1+1;
}//end outer else
ind=ind+1;
}//end while
for (int i = i0; i < len0; i = i + 1) {
united[ind] = th0[i];
ind = ind + 1;
}
for (int i = i1; i < len1; i = i + 1) {
united[ind] = th1[i];
ind = ind + 1;
}for (int i = i2; i < len2; i = i + 1) {
united[ind] = th2[i];
ind = ind + 1;
}
return united;
}
static int[] merge3sort(int[] m) { //function that glues all together
if (m.length == 1) {
return m;
}
else{
return merge(merge3sort(split(m,m.length/3)),merge3sort(split(m,m.length/3)),merge3sort(split(m,m.length/3))); }
}
I get the following exception:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at ololosh1.Ex3.split(Ex3.java:27)
at ololosh1.Ex3.merge3sort(Ex3.java:98)
at ololosh1.Ex3.main(Ex3.java:15)

Look at this part of your code:
for(int i = 0; i<=m.length/3; i++)
third[i]=m[i];
for(int i=0; i<=m.length/3;i++)
third1[i]=m[i+thirdNum];
for(int i=0; i<=m.length/3;i++)
third2[i]=m[i+2*thirdNum];
Arrays are indexed from 0 to length-1. Each third* array has length m.length/3. Therefore their index can only go up to m.length/3 - 1. Yet you are indexing up to and including m.length/3.
Once you get your application working correctly, you really should clean it up. There is a lot of redundancy. For example, you are using the expression m.length/3 multiple times in method split() but you are also passing that same value to it as an argument.