We Keep Coding

How do I replace zeros in a matrix?

Replace the elements with a value of 0.0 with the average of the adjacent elements: previous and / or next in the same row.
Here's my code. Can u help me to solve it?
public void replaceZeros(double[][] array){
for (int i = 0; i < array.length; i++){
for(int j = 0; i < array[i].length; j++){
if(array[i][j] == 0){
if(array[i][0] == 0){
array[i][j] = array[i+1][j];
} else if(j == array[i].length-1){
array[i][j] = array[i-1][j];
} else {
array[i][j] = (array[i+1][j]+array[i-1][j])/2;
}
}
}
}
}

If I understand correctly, you want to replace elements of an array that are 0 with the average of a neighbour to the left and right. In the code you provided, you increase and decrease second array argument which is the column. Try this code:
public void replaceZeros(double[][] array) {
for (int i = 0; i < array.length; i++) {
for (int j = 0; i < array[i].length; j++) {
if (array[i][j] == 0) {
//check if its first element in a row
if (j == 0) {
array[i][j] = array[i][j + 1];
}
//check if its last element in a row
else if (j == array[i].length - 1) {
array[i][j] = array[i][j - 1];
}
//proceed with calculating average
else {
array[i][j] = (array[i][j + 1] + array[i][j - 1]) / 2;
}
}
}
}
}

Your for loop had minor issues, below for loop should work :
public void replaceZeros(double[][] array){
for (int i = 0; i < array.length; i++){
for(int j = 0; j < array[i].length; j++){
if(array[i][j] == 0) { // If element is 0
if (j == 0) { // If element is in 1st column, any row
array[i][j] = array[i][j+1];
} else if(j == array[i].length-1) { // If element is in last column, any row
array[i][j] = array[i][j-1];
} else { // If element is not in 1st or last column, any row
array[i][j] = (array[i][j-1]+array[i][j+1])/2;
}
}
}
}
}

How can I check if every single int in a randomly generated array is even and make it create another random array if it's not?

So I'm trying to create a program that creates a randomly generated array with numbers between 0 and 10.
Every time a number inside the 4x4 array is odd I want it to generate a brand new array and print every array discarded aswell until it creates a 4x4 array with only even numbers.
The problem right now is that I can't understand how to fix the last for and make it work properly with the boolean b that is supposed to restart the creation of the array.
import java.util.Scanner;
public class EvenArrayGenerator {
public static void main(String a[]) {
Boolean b;
do {
b = true;
int[][] Array = new int[4][4];
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++)
Array[i][j] = (int) (Math.random() * 11);
}
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
System.out.print(Array[i][j] + " ");
}
System.out.println();
}
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
if (Array[i][j] % 2 != 0)
b = false;
}
}
} while (b);
}
}

public class ArrayGen {
private int[][] array = new int[4][4];
private int iterations = 1; // you always start with one iteration
public static void main (String[] args) {
ArrayGen ag = new ArrayGen();
ag.reScramble();
while(!ag.isAllEven()) {
ag.reScramble();
ag.iterations++;
}
// this is just a nice visualisation
for (int i = 0; i < 4; i++) {
System.out.print("[");
for (int j = 0; j < 4; j++) {
System.out.print(ag.array[i][j] +((j != 3)? ", " : ""));
}
System.out.print("]\n");
}
System.out.println(ag.iterations + " iterations needed to get all-even array.");
}
private void reScramble () {
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
array[i][j] = (int)(Math.random() * 11);
}
}
}
private boolean isAllEven () {
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
if (array[i][j] % 2 == 1) {
return false;
}
}
}
return true;
}
}
I think this is a good solution. Refactoring your code into structured methods is never a bad idea. I hope this helps!

You are looping until you get an array that's all even. You should initialize b to be false, and update it to true in the (nested) for loop. Note that once's you've set it to false, there's no reason checking the other members of the array, and you can break out of the for loop.
Note, also, that using stream could make this check a tad more elegant:
b = Arrays.stream(arr).flatMapToInt(Arrays::stream).anyMatch(x -> x % 2 != 0)

What about generating random numbers up to 5 and double it? Then you don't have two check if they are even.

Instead of your last for loop:
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
if(Array[i][j] % 2!=0){
b=false;
break;
}
}
if(!b){
break;
}
}
if(!b){
break;
}
Alternatively, you could do an oddity check when you are generating the elements. Something like:
int element;
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
do{
element = (int)(Math.random()*11);
}while(element % 2 !=0)
Array[i][j] = element;
}
}
That way you don't have to check the values, they will always be even.

This should work:
import java.util.Scanner;
public class EvenArrayGenerator{
public static void main(String a[]){
boolean anyOdd;
int array = 0;
do{
System.out.println ("Array " + ++array + ":");
anyOdd=false;
int[][] Array = new int[4][4];
for(int i=0;i<4;i++) {
for(int j=0;j<4;j++) {
Array[i][j] = (int)(Math.random()*11);
}
}
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
System.out.print(Array[i][j] + " ");
}
System.out.println();
}
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
anyOdd |= Array[i][j] % 2!=0;
}
}
} while(anyOdd);
}
}
As you can see, I just modified the condition from b to anyOdd, so if there is any odd number, it will iterate again.
Also, you can check it when you generate the random numbers, so you avoid a second loop:
import java.util.Scanner;
public class EvenArrayGenerator{
public static void main(String a[]){
boolean anyOdd;
int array = 0;
do{
System.out.println ("Array " + ++array + ":");
anyOdd=false;
int[][] Array = new int[4][4];
for(int i=0;i<4;i++) {
for(int j=0;j<4;j++) {
Array[i][j] = (int)(Math.random()*11);
anyOdd |= array[i][j] % 2 != 0;
}
}
for(int i=0;i<4;i++){
for(int j=0;j<4;j++){
System.out.print(Array[i][j] + " ");
}
System.out.println();
}
} while(anyOdd);
}
}

public class EvenArrayGenerator {
public static void main(String a[]) {
int[][] arr = createAllEvenArray(4);
printArray(arr);
}
private static int[][] createAllEvenArray(int size) {
while (true) {
int[][] arr = createArray(size);
printArray(arr);
if (isAllEven(arr))
return arr;
}
}
private static int[][] createArray(int size) {
int[][] arr = new int[size][size];
for (int i = 0; i < arr.length; i++)
for (int j = 0; j < arr.length; j++)
arr[i][j] = (int)(Math.random() * 11);
return arr;
}
private static void printArray(int[][] arr) {
for (int i = 0; i < 4; i++) {
for (int j = 0; j < 4; j++) {
if (j > 0)
System.out.print("\t");
System.out.format("%2d", arr[i][j]);
}
System.out.println();
}
System.out.println();
}
private static boolean isAllEven(int[][] arr) {
for (int i = 0; i < arr.length; i++)
for (int j = 0; j < arr.length; j++)
if (arr[i][j] % 2 != 0)
return false;
return true;
}
}

No three same in row

Task: Given an integer denoting the size of the array.Fill array with integers.
Return true,if the array contains three of same elements not next to each other.
Return false,if the array not contains three of same elements,or contains but next to each other.
public static boolean noThreeInRow(int [] array){
for(int i = 0; i < array.length-1; i++){
if(array.length < 3) System.exit(0);
if(array[i] != array[i+1]){
return true;
}else return false;
}return true;
}
I can't solved this problem.Someone could help me?I am very beginner!

try using a counter and two loops to compare each number.
int counter = 0;
for(int i = 0; i < array.length-1; i++){
if(array.length < 3) System.exit(0);
for (int j = 0; j < array.length-1; j++){
if (array[i] == array [j+2]) counter ++
}
return true
}return true;
Try something like that. But you will have to figure out how to deal with the numbers before array[i] during the j loop. Happy Coding :)

How to check array for possible divisors?

Creating the array, I am letting the user choose the length:
StartNum = scan.nextInt();
int[] NumBox = new int[StartNum];
for (int i = 1; i < NumBox.length+1; i++)
{NumBox[i - 1] = i;}
NumBox[0]=0;
Assuming there are other methods that can change cells in NumBox to 0, how would I use a for loop to check each cells in the array for any divisor? If there are no divisors for the cell in the array, it will then become a 0. For example, if the array is [0,2,0,4,0,6,7,8,9] 9,2 and 7 would become a 0.
The code below is what I tired but didn't get far.
boolean NoDiv=false;
for (int a=1; a < NumBox.length+1; a++)
{
a++
for (int check=1; a < NumBox.length+1; check++)
{
if (NumBox[a-1]% check == 0 && NumBox[a-1] !=0)
{
NumBox[a-1] = 0;
}
}
}

for (int i = 0; i < NumBox.length; i++) {
if (NumBox[i] == 0) continue;
boolean hasDivisor = false;
for (int j = 0; j < i; j++) {
if (NumBox[j] == 0) continue;
if (NumBox[i] % NumBox[j] == 0) {
hasDivisor = true;
break;
}
}
if (!hasDivisor) NumBox[i] = 0;
}

Having Trouble using For Loops to make two triangles of different characters fit into a rectangle?

Examples of input:
3
4
Examples of output (assume that spaces = new lines.)
QQQH
QQHH
QHHH
QQQQH
QQQHH
QQHHH
QHHHH
So far, the fragment of code that attempts to print this is (Assume that all variables are pre-defined):
public int getSize()
{
for (int i = size; i > 0; i--){
for (int j = 1; j < size; j++){
out.print("Q");
out.print("H");
}
out.println("");
}
return 0;
}
It just prints: (assume that spaces = new lines.)
QHQHQHQHQH
QHQHQHQHQH
QHQHQHQHQH
QHQHQHQHQH
QHQHQHQHQH
For input of 5. I'm not quite sure how to make it print only the number of times of its respective integer value. Can someone explain?

You could break the inner loop it two, like this:
for (int i = size; i > 0; i--) {
for (int j = 0; j < i; j++) {
out.print("Q");
}
for (int j = i; j < size + 1; j++) {
out.print("H");
}
out.println();
}
Output:
QQQH
QQHH
QHHH
QQQQH
QQQHH
QQHHH
QHHHH
Or if you don't want to break the loop, you can use the ternary operator:
for (int i = size; i > 0; i--) {
for (int j = 0; j < size + 1; j++) {
out.print(j < i ? 'Q' : 'H');
}
out.println();
}

Try this
for (int i = 0; i < size; i++) {
for (int j = 1; j <= size-i; j++) {
System.out.print("Q");
}
for (int k = 0; k <= i; k++) {
System.out.print("H");
}
System.out.println("");
}

try this code block instead:
int j=0;
for (int i = size; i > 0; i--)
{
j=0;
while(j < i)
{
out.print("Q");
j++;
}
j=i;
while(j < size+ 1)
{
out.print("H");
j++;
}
out.println();
}

Tested with sample inputs. Working fine
public int getSize() {
for (int i = 1; i < size+1; i++) {
for (int j = 0; j < size+1; j++) {
int Qtimes = size-i;
if(j <= Qtimes) {
System.out.print("Q");
} else{
System.out.print("H");
}
}
System.out.println("");
}
return 0;
}

This works if the input is 4 - for example -change it to any number
public int getSize()
{
int cnt = 0;
int i,j,k = 0;
for ( i = 4; i > 0; i--){
for ( j = 0; j < i; j++){
System.out.print("Q");
}
cnt ++;
for( k = 0 ; k <cnt ; k++) {
System.out.print("H");
}
System.out.println("");
}
return 0;
}
output is
QQQQH
QQQHH
QQHHH
QHHHH