I am having trouble creating multiple arrays with a loop in Java. What I am trying to do is create a set of arrays, so that each following array has 3 more numbers in it, and all numbers are consecutive. Just to clarify, what I need to get is a set of, let's say 30 arrays, so that it looks like this:
[1,2,3]
[4,5,6,7,8,9]
[10,11,12,13,14,15,16,17,18]
[19,20,21,22,23,24,25,26,27,28,29,30]
....
And so on. Any help much appreciated!
Do you need something like this?
int size = 3;
int values = 1;
for (int i = 0; i < size; i = i + 3) {
int[] arr = new int[size];
for (int j = 0; j < size; j++) {
arr[j] = values;
values++;
}
size += 3;
int count = 0;
for (int j : arr) { // for display
++count;
System.out.print(j);
if (count != arr.length) {
System.out.print(" , ");
}
}
System.out.println();
if (i > 6) { // to put an end to endless creation of arrays
break;
}
}
To do this, you need to keep track of three things: (1) how many arrays you've already created (so you can stop at 30); (2) what length of array you're on (so you can create the next array with the right length); and (3) what integer-value you're up to (so you can populate the next array with the right values).
Here's one way:
private Set<int[]> createArrays() {
final Set<int[]> arrays = new HashSet<int[]>();
int arrayLength = 3;
int value = 1;
for (int arrayNum = 0; arrayNum < 30; ++arrayNum) {
final int[] array = new int[arrayLength];
for (int j = 0; j < array.length; ++j) {
array[j] = value;
++value;
}
arrays.add(array);
arrayLength += 3;
}
return arrays;
}
I don't think that you can "create" arrays in java, but you can create an array of arrays, so the output will look something like this:
[[1,2,3],[4,5,6,7,8,9],[10,11,12,13...]...]
you can do this very succinctly by using two for-loops
Quick Answer
==================
int arrays[][] = new int[30][];
for (int j = 0; j < 30; j++){
for (int i = 0; i < (j++)*3; i++){
arrays[j][i] = (i++)+j*3;
}
}
the first for-loop tells us, via the variable j, which array we are currently adding items to. The second for-loop tells us which item we are adding, and adds the correct item to that position.
All you have to remember is that j++ means j + 1.
Now, the super long-winded explanation:
I've used some simple (well, I say simple, but...) maths to generate the correct item each time:
[1,2,3]
here, j is 0, and we see that the first item is one. At the first item, i is also equal to 0, so we can say that, here, each item is equal to i + 1, or i++.
However, in the next array,
[4,5,6,7,8,9]
each item is not equal to i++, because i has been reset to 0. However, j=1, so we can use this to our advantage to generate the correct elements this time: each item is equal to (i++)+j*3.
Does this rule hold up?
Well, we can look at the next one, where j is 2:
[10,11,12,13,14...]
i = 0, j = 2 and 10 = (0+1)+2*3, so it still follows our rule.
That's how I was able to generate each element correctly.
tl;dr
int arrays[][] = new int[30][];
for (int j = 0; j < 30; j++){
for (int i = 0; i < (j++)*3; i++){
arrays[j][i] = (i++)+j*3;
}
}
It works.
You have to use a double for loop. First loop will iterate for your arrays, second for their contents.
Sor the first for has to iterate from 0 to 30. The second one is a little less easy to write. You have to remember where you last stop and how many items you had in the last one. At the end, it will look like that:
int base = 1;
int size = 3;
int arrays[][] = new int[30][];
for(int i = 0; i < 30; i++) {
arrays[i] = new int[size];
for(int j = 0; j < size; j++) {
arrays[i][j] = base;
base++;
}
size += 3;
}
Related
The first 4 values are set properly in the new array. It has to do with something with my variable 'count' which is not being set properly. The goal of the program is to simply grab the even numbers, and put them in a new array.
I have added 4 to count as a test, and that seems to work perfectly but I dont think that is the issue here.
int[] list = {8,5,4,11,12,2,1,3,10,6,7};
int count = 0;
int gr = 0;
for(int n=0; n<list.length; n++)
{
if(list[n] % 2 == 0)
{
count++;
}
}
int[] evn = new int[count];
for(int k = 0; k<=count; k++)
{
if(list[k] % 2 == 0)
evn[gr++] = list[k];
}
return evn;
Currently, the array prints "8,4,12,2,0,0" when it should print "8,4,12,2,10,6"
This happens because count is always less than the size of the array(list.length), so in the second for-loop you are never iterating till the end of the array.
Change your second for-loop to iterate till the end of the array as shown below :
for(int k = 0; k < list.length; k++)
You're only traversing part of list, as stated in the for condition:
for(int k = 0; k<=count; k++)
^--here--^
This is because count has a lower value than the length of the original array. Change this condition to traverse the whole array:
for(int k = 0; k<list.length; k++)
To traverse the whole list change the following:
for(int k = 0; k<=count; k++)
To
for(int k = 0; k<list.length; k++)
I want to convert ArrayList to Array 2-Dimension
I have the code below:
ArrayList<String> arrayList=new ArrayList();
arrayList.add("A")
arrayList.add("B")
arrayList.add("C")
arrayList.add("D")
arrayList.add("E")
arrayList.add("F")
int nSize=0,n3item=0, remain=0;
nSize=arrayList.size();
n3item=nSize/3;
remain=nSize%3;
String[][] array[n3item][3]
I want to convert ArrayList to array for example
array[0][1]="A"
array[0][2]="B"
array[0][3]="C"
array[1][1]="D"
array[1][2]="E"
array[1][3]="F"
Now I haven't a solution to do this.
In case of remain is not 0. How to give a solution to this problem
I need your help.
Thanks.
You can use a simple nested for-loop to achieve this.
int numCol = 3;
int numRow = (int) Math.ceil(arrayList.size() / ((double) numCol));
String[][] array = new String[numRow][numCol];
int i, j;
for (i = 0; i < numRow; i++) {
for (j = 0; j < 3 && (i * numCol + j) < arrayList.size(); j++) {
array[i][j] = arrayList.get((i * numCol) + j);
}
}
numRow is found by taking the ceil of number of elements in the list divided by num of desired columns.
eg - when arraylist has 7 elements, numRow will be ceil(7/3.0) = 3.
The main trick here is in the inner for-loop condition (i * numCol + j) < arrayList.size(). It enables us to terminate the loop for the condition remain != 0 you mentioned.
Try to think, how you can fill the 2D array with arraylist values. You need to use a nested loop for assigning the values into the 2D array. Outer loop will iterate over the rows and inner loop will fill the values into each 1D array.
int index = 0;
for(int i = 0; i < n3item; i++) {
for(int j = 0; j < 3; j++) {
array[i][j] = arrayList.get(index);
index++;
}
}
The question is:
Create a method display2DArray().
a) Inside the method, declare a 2D array that will hold the following integers:
{10,20} {11,21}
{15,25} {17,28}.
b) Display this information using two for loops.
public static void display2DArray()
{
int[][] arrays = new int[][]
{
{10, 20}, {11,21}, {15,25}, {17,28}
};
for(int i = 0; i < 3; i++)
{
for(int j = 0; i < 1; j++)
{
System.out.println(arrays[i][j]);
}
}
}
This is what ive come up with, but its not correct.
Can someone tell me what i need to be doing?
You are almost there!
Few things:
1) Typo - In your inner for loop, you are using an "j" instead of "i".
2) The same "j" must be j<=1 OR j<2 because you have 2 columns i.e. 2 elements in each sub-array. So the indexes will be 0 and 1.
3) In your outer for loop, you are using i<3. Since you have 4 rows i.e. 4 sub arrays, your indexes will be 0,1,2,3. So you need to use i<=3 OR i<4.
4) You can print an empty line in the outer for-loop for a better display.
for(int i = 0; i <= 3; i++) // Since you have 4 rows, indexes would be 0,1,2,3
{
for(int j = 0; j <= 1; j++) // Since you have 2 columns, indexes would be 0,1
{
System.out.print(arrays[i][j]+","); // Print each row i.e. sub-array
}
System.out.println(""); // Print an empty line after each row
}
This gives you the output:
10,20,
11,21,
15,25,
17,28,
In your second for loop, you have "i < 1" instead of "j < 1"
Use j in second array
public static void display2DArray()
{
int[][] arrays = new int[][]
{
{10, 20}, {11,21}, {15,25}, {17,28}
};
for(int i = 0; i < 4; i++)
{
for(int j = 0; j < 2; j++)
{
System.out.println(arrays[i][j]);
}
}
}
Also the boundaries were wrong
Your Problem with the inner loop the you used . You used i instead of J. So, Your loop will not give you the result as you Expected.
for(int i = 0; i < 3; i++)
{
for(int j = 0; j <= 1; j++) //use j instead of i here.
{
System.out.println(arrays[i][j]);
}
}
Thanks
for(int i = 0; i <= 3; i++)
{
for(int j = 0; j <= 1; j++)
{
System.out.println(arrays[i][j]);
}
}
1.) second for loop condition check is j< 1 not i< 1
2.) first for loop condition check is i<=3
Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 8 years ago.
Improve this question
I want to create a union array for two integer arrays using nested loops.
This is my attempt so far:
import java.util.Scanner ;
public class array4 {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter first array size:");
int size = input.nextInt();
int x[] = new int[size];
System.out.println("Enter first array elements:");
for (int i = 0; i < size; i++) {
x[i] = input.nextInt();
}
System.out.print("Enter second array size:");
int size2 = input.nextInt();
int y[] = new int[size2];
for (int i = 0; i < size2; i++) {
y[i] = input.nextInt();
}
System.out.println("Union");
for (int i = 0; i < size; i++) {
System.out.println(x[i]);
}
for (int i = 0; i < size2; i++) {
for (int z = 0; z < size; z++) {
if (y[i] != x[z]) {
System.out.println(y[i]);
}
}
}
}
}
Lets assume that we will print all numbers from second array, and only these numbers from first array which don't exist in second one. So
for each element in first array
test if it exist in second array (iterate over elements in second array and set some boolean flag like exists to true if x[i]==y[j])
if element doesn't exist in second array print it
iterate over elements from second array
and print them
Algorithm can look like
for (int i = 0; i <= x.length; i++) {// "<=" is not mistake,
// in last iteration we print all elements
// from second array
boolean exist = false;
for (int j = 0; j < y.length; j++) {
if (i < x.length) {
if (x[i] == y[j])
exist = true;
} else
System.out.println(y[j]);
}
if (!exist && i < x.length)
System.out.println(x[i]);
}
This algorithm can be probably rewritten to something simpler but I will leave it in this form for now.
For the lack of requirements, here is my answer for now... just basing on your current code.
for (int i = 0; i < size2; i++) {
for (int z = 0; z < size; z++) {
if (y[i] != x[z]) {
System.out.println(y[i]);
break; //added break
}
}
}
The problem was you're printing array elements without duplicate multiple times, to avoid that, you should add a break after you print the element with no duplicate.
By the way, your code is just printing the elements on both arrays, I thought you're suppose to combine them? Shouldn't you have a new array that contains both of the elements on the two arrays?
EDIT 2:
Add these lines of code after you get the two set of arrays without duplicate:
I also added comments to explain what's happening.
System.out.println("Union");
int[] unionArray = new int[size + size2]; //created a new array that will contain two arrays
for (int i = 0; i < size; i++) { //put the first set of int in the new array
unionArray[i] = x[i];
}
for (int i = size; i < unionArray.length; i++) { //put the second set
unionArray[i] = y[i-size]; //i = size : started with the last index of the first array
//y[i-size] : we are getting the elements on the second array
}
for (int i = 0; i < unionArray.length; i++) { //output
System.out.println(unionArray[i]);
}
Hope this helps. :)
If it's just to play with arrays and you don't need to use loops - try using a Java collection for that task, that's how most people would probably implement it:
init collection 1 from array 1
init collection 2 from array 2
add collection 2 to collection 1
convert collection 1 back to an array
That can be a (more or less) neat one-liner.
This question already has answers here:
How do I reverse an int array in Java?
(47 answers)
Closed 8 years ago.
I have an array of n elements and these methods:
last() return the last int of the array
first() return the first int of the array
size() return the length of the array
replaceFirst(num) that add the int at the beginning and returns its position
remove(pos) that delete the int at the pos
I have to create a new method that gives me the array at the reverse order.
I need to use those method. Now, I can't understand why my method doesn't work.
so
for (int i = 1; i
The remove will remove the element at the position i, and return the number that it is in that position, and then with replaceFirst will move the number (returned by remove) of the array.
I made a try with a simple array with {2,4,6,8,10,12}
My output is: 12 12 12 8 6 10
so if I have an array with 1,2,3,4,5
for i = 1; I'm gonna have : 2,1,3,4,5
for i=2 >3,2,1,4,5
etc
But it doesn't seem to work.
Well, I'll give you hints. There are multiple ways to reverse an array.
The simplest and the most obvious way would be to loop through the array in the reverse order and assign the values to another array in the right order.
The previous method would require you to use an extra array, and if you do not want to do that, you could have two indices in a for loop, one from the first and next from the last and start swapping the values at those indices.
Your method also works, but since you insert the values into the front of the array, its going to be a bit more complex.
There is also a Collections.reverse method in the Collections class to reverse arrays of objects. You can read about it in this post
Here is an code that was put up on Stackoverflow by #unholysampler. You might want to start there: Java array order reversing
public static void reverse(int[] a)
{
int l = a.length;
for (int j = 0; j < l / 2; j++)
{
int temp = a[j]
a[j] = a[l - j - 1];
a[l - j - 1] = temp;
}
}
int[] reverse(int[] a) {
int len = a.length;
int[] result = new int[len];
for (int i = len; i > 0 ; i--)
result[len-i] = a[i-1];
return result;
}
for(int i = array.length; i >= 0; i--){
System.out.printf("%d\n",array[i]);
}
Try this.
If it is a Java array and not a complex type, the easiest and safest way is to use a library, e.g. Apache commons: ArrayUtils.reverse(array);
In Java for a random Array:
public static void reverse(){
int[] a = new int[4];
a[0] = 3;
a[1] = 2;
a[2] = 5;
a[3] = 1;
LinkedList<Integer> b = new LinkedList<Integer>();
for(int i = a.length-1; i >= 0; i--){
b.add(a[i]);
}
for(int i=0; i<b.size(); i++){
a[i] = b.get(i);
System.out.print(a[i] + ",");
}
}
Hope this helps.
Reversing an array is a relatively simple process. Let's start with thinking how you print an array normally.
int[] numbers = {1,2,3,4,5,6};
for(int x = 0; x < numbers.length; x++)
{
System.out.println(numbers[x]);
}
What does this do? Well it increments x while it is less than numbers.length, so what is actually happening is..
First run : X = 0
System.out.println(numbers[x]);
// Which is equivalent to..
System.out.println(numbers[0]);
// Which resolves to..
System.out.println(1);
Second Run : X = 1
System.out.println(numbers[x]);
// Which is equivalent to..
System.out.println(numbers[1]);
// Which resolves to..
System.out.println(2);
What you need to do is start with numbers.length - 1, and go back down to 0. To do this, you need to restructure your for loop, to match the following pseudocode..
for(x := numbers.length to 0) {
print numbers[x]
}
Now you've worked out how to print, it's time to move onto reversing the array. Using your for loop, you can cycle through each value in the array from start to finish. You'll also be needing a new array.
int[] revNumbers = new int[numbers.length];
for(int x = numbers.length - 1 to 0) {
revNumbers[(numbers.length - 1) - x] = numbers[x];
}
int[] noArray = {1,2,3,4,5,6};
int lenght = noArray.length - 1;
for(int x = lenght ; x >= 0; x--)
{
System.out.println(noArray[x]);
}
}
int[] numbers = {1,2,3,4,5};
int[] ReverseNumbers = new int[numbers.Length];
for(int a=0; a<numbers.Length; a++)
{
ReverseNumbers[a] = numbers.Length - a;
}
for(int a=0; a<ReverseNumbers.Length; a++)
Console.Write(" " + ReverseNumbers[a]);
int[] numbers = { 1, 2, 3, 4, 5, 6 };
reverse(numbers, 1); >2,1,3,4,5
reverse(numbers, 2); >3,2,1,4,5
public int[] reverse(int[] numbers, int value) {
int index = 0;
for (int i = 0; i < numbers.length; i++) {
int j = numbers[i];
if (j == value) {
index = i;
break;
}
}
int i = 0;
int[] result = new int[numbers.length];
int forIndex = index + 1;
for (int x = index + 2; x > 0; x--) {
result[i] = numbers[forIndex--];
++i;
}
for (int x = index + 2; x < numbers.length; x++) {
result[i] = numbers[x];
++i;
}
return result;
}