We Keep Coding

printing numbers with nested loops

I have to print the following numbers using nested loops, and I kinda have an idea how, but not how to execute it.
000111222333444555666777888999
000111222333444555666777888999
000111222333444555666777888999
My code so far is something like:
public class opgave_2 {
public static void main(String[] args) {
final int first = 3;
final int second = 3;
final int third = 9;
for (int i = 0; i <= first ; i++) {
for (int j = i; j <= second; j++) {
for (int k = j; k <= third; k++) {
System.out.print(i);
}
}
}
}
}

You should proceed by steps to resolve such problem.
First, you want to print a number 3 times :
int myNumber = 0;
for(int i=0; i<3; i++) {
System.out.print(myNumber);
}
Second, you want to repeat it 9 times and your number to vary from 0 to 9 (seems like an index of loop) :
for(int myNumber=0; myNumber<=9; myNumber++) {
for(int i=0; i<3; i++) {
System.out.print(myNumber);
}
}
Third, you want to display this line 3 times :
for(intj=0; j<3; j++) {
for(int myNumber=0; myNumber<=9; myNumber++) {
for(int i=0; i<3; i++) {
System.out.print(myNumber);
}
}
System.out.println(""); //new line
}

What about something like this:
for (int i = 0; i < 3; i++) {
for (int j = 0; j <= 9; j++) {
System.out.printf("%1$s%1$s%1$s", j);
}
System.out.println();
}
Which uses 2 nested loops. The first to print the line 3 times, and the second to print the numbers per line

you can use a loop, that loops 3 times. in that you put a loop that prints every number from 0 to 9 3 times in a row within the same line
for(int a = 0; a < 3; a++){
for(int i = 0; i < 10; i++){
System.out.print(i+""+i+""+i);
}
System.out.println(); //for the new line
}
or
for(int a = 0; a < 3; a++){
for(int i = 0; i < 10; i++){
System.out.print(i);
System.out.print(i);
System.out.print(i);
}
System.out.println(); //for the new line
}
this should do

Making a single number per line pyramid using nested loop and trying to center it

I have to create a number pyramid using nested loops for homework. I am very new to nested loops and am still not quite clear on how they work completely. My objective is to make this pyramid using nested loops:
-----1-----
----333----
---55555---
--7777777--
-999999999-
however I have only been able to get this:
----------1
--------333--
------55555----
----7777777------
--999999999--------
I think I am on the right track but I am not sure where to go from here.
Here is the code I currently have:
public class NumberPyramid
{
public static void main(String [] args)
{
for(int i=1; i<=9; i+=2)
{
for (int j = 11; j > i; j--)
{
System.out.print("-");
}
for(int j=1; j<=i; j++)
{
System.out.print(i);
}
for (int j = 1; j < i; j++)
{
System.out.print("-");
}
System.out.println();
}
}
}

The part of printing the numbers in the center is correct.
Printing the - before and after the numbers is incorrect.
Notice that for any row, the number of - before and after the numbers should be the same. How many - to print for a number?
For 1, print 5 - before and after.
For 3, print 4 - before and after.
For 5, print 3 - before and after.
That's (11 - i) / 2. Put this loop before and after the center line and you're done.
for (int j = 0; j < (11 - i) / 2; j++) {
System.out.print("-");
}

You should remove two - on every second line
int index = 5;
for (int i=1; i<=9; i+=2) {
for (int j=0; j<index; j++) {
System.out.print("-");
}
for (int k=0; k<i; k++) {
System.out.print(i);
}
for (int j=0; j<index; j++) {
System.out.print("-");
}
System.out.println();
index--;
}

Java - Hourglass

I'm missing by just a little bit. What I want:
*******
*****
***
*
***
*****
*******
What I'm getting
*******
*****
***
*
*
***
*****
*******
The code
public class HD404 {
public static void main(String[] args) {
int N = StdIn.readInt();
int x = N*2-1;
for (int i = 0; i < N; i++) {
for (int j = i; j > 0; j--) {
StdOut.print(" ");
}
for (int k = 0; k < x; k++) {
StdOut.print("*");
}
x-=2;
StdOut.println();
}
x = 1;
for (int i = 0; i < N; i++) {
for (int j = i; j < N-1; j++) {
StdOut.print(" ");
}
for (int k = 0; k < x; k++) {
StdOut.print("*");
}
x += 2;
StdOut.println();
}
}
}
Right now I'm mostly just guessing and I just can't pin point my error. What am I missing here?

The problems lays with the second part of your code where you ask to draw one star and you start at zero where you should start at one.
Solution
x = 1;
for (int i = 0; i < N; i++)
should be replaced with
x = 3;
for (int i = 1; i < N; i++)

The problem is that you are starting to draw the bottom of the hourglass with 1 asterisk (x = 1) instead of 3.
The second issue is that the bottom of the hourglass only has N-2 lines, not N-1 so the loop should start at 1 instead of 0. This is because the line with a single asterisk was already drawn in the upper-half.
Corrected code:
public static void main(String[] args) {
int N = StdIn.readInt();
int x = N*2-1;
for (int i = 0; i < N; i++) {
for (int j = i; j > 0; j--) {
StdOut.print(" ");
}
for (int k = 0; k < x; k++) {
StdOut.print("*");
}
x-=2;
StdOut.println();
}
x = 3; // <-- not 1 here, the first line has 3 asterisks
for (int i = 1; i < N; i++) { // <-- i starts at 1 because the first line was already drawn in the upper half
for (int j = i; j < N-1; j++) {
StdOut.print(" ");
}
for (int k = 0; k < x; k++) {
StdOut.print("*");
}
x += 2;
StdOut.println();
}
}
As a side-note, you could rewrite this code a lot shorter by making the following observations:
There are x lines to draw so we can loop from 0 to x included (to respect the symmetry) and skip the middle line so as not to draw it twice
For every line, there are x columns to draw and it is either a space or a *.
For every line, * is drawn only if the current column is between min(i, x-i) and max(i, x-i) (if we're in the upper-part, i < x-i and if we're in the bottom-part, i > x-i).
Code:
public static void main(String[] args) {
int N = 4;
int x = 2 * N - 1;
for (int i = 0; i <= x; i++) {
if (i == N) continue; // skip the middle-line for it not to be drawn twice
for (int j = 0; j < x; j++) {
System.out.print(j >= Math.min(i, x-i) && j < Math.max(i, x-i) ? "*" : " ");
}
System.out.println();
}
}
Sample output:
*******
*****
***
*
***
*****
*******

The easiest way I can think up is probably to prevent the last iteration of your first outer loop, that way you'll prevent the first single star line to be shown.
I would probably do it this way:
for(int i = 0; i < N && x > 1; i++)
{
/*Code of the first inner loop*/
}

For those whose still looking for a simpler and lesser code regarding hourglass challenge. This contains 2 for loops only.
You may use this as reference.
public static void hourGlass(int size) {
// 2 for loops only
int dimension = (size * 2) - 1, space = 0, stars = size - 1, printed = 0;
for(int i=0; i<dimension; i++) {
int actual = space;
for (int j=dimension; j > 0; j--) {
if(actual > 0) {
System.out.print(" ");
actual--;
}
else {
System.out.print("*");
if(stars==printed) {
actual = space;
printed = 0;
} else {
actual = 1;
printed++;
}
}
}
if(i <= size-2) { // will pattern spaces and stars from top to middle
space++;
stars--;
}
else { // will pattern spaces and stars from middle to top
space--;
stars++;
}
System.out.println();
}
}

Using for loops to create an upside-down triangle [duplicate]

This question already has answers here:
Creating a triangle with for loops
(13 answers)
Closed 8 years ago.
Im a java student, and i'm have quite the hard time, trying to use for loops to create an upside down triangle.
This is what my code looks like now, a straight forward triangle. How can i make another one just like it, but upside down?
for (int i=1; i<20; i += 2)
{
for (int k=10; k < (0 - i / 2); k++)
{
System.out.print(" ");
}
for (int j=0; j<i; j++)
{
System.out.print("*");
}
System.out.println("");
}

Is that tricky?
Just change
for (int i=1; i<20; i += 2)
To
for (int i = 19; i >0; i -= 2)
Code.
for (int i = 19; i > 0; i -= 2) {
for (int k = 10; k < (0 - i / 2); k++) {
System.out.print(" ");
}
for (int j = 0; j < i; j++) {
System.out.print("*");
}
System.out.println("");
}
Out put:
*******************
*****************
***************
*************
***********
*********
*******
*****
***
*

int c = 2*lines;
for (int i = lines-1; i>=0; i--)
{
for (int j = i; j < lines; j++)
{
System.out.print(" ");
}
for (int k = 1; k <= c; k++)
{
if (k % 2 == 0)
{
System.out.print(" ");
}
else
{
System.out.print(symbol);
}
}
System.out.print("\n");
c -= 2;
}

All you have to do is to change your 3rd for loop
for (int j=0; j<i; j++)
{
System.out.print("*");
}
In your code, you print 1 star, 3 stars, 5 stars and so on... (i stars actually)
To make it upside down, start the j at the max value and decrement it so you print n - i stars
for (int j = 20 - i; j > 0; j--)
{
System.out.print("*");
}

public static void main(String[] args) {
StringBuffer sb = new StringBuffer();
for (int i = 1; i < 20; i += 2) {
for (int k = 10; k < (0 - i / 2); k++) {
sb.append(" ");
}
for (int j = 0; j < i; j++) {
sb.append("*");
}
sb.append("\n");
}
System.out.println(sb.reverse());
}
However you are probably supposed to learn something about loops and the algorithm.

Printing a triangle in Java

I'm practicing basic coding exercises and trying to print the following triangle in Java:
*
***
*****
***
*
The following code gives me the results but I feel like there must be a much more elegant solution
for (int i = 1; i <= 5; i++) {
if (i % 2 == 1) {
for (int j = 1; j <= i; j++) {
System.out.print("*");
}
System.out.println("");
}
}
for (int i = 3; i > 0; i--) {
if (i % 2 == 1) {
for (int j = 1; j < i + 1; j++) {
System.out.print("*");
}
System.out.println("");
}
}
Can anyone provide some insight into how to make this work in a better way?
Ok, here's some more code that produces the correct result that uses just the two for loops, but it looks even uglier:
for (int i = 1; i <= 10; i += 2) {
if (i <= 5) {
for (int j = 1; j <= i; j++) {
System.out.print("*");
}
System.out.println("");
}
else if(i > 5 && i < 8){
for(int j = i/2; j > 0; j--){
System.out.print("*");
}
System.out.println("");
}
else{
for(int j = 1; j > 0; j--){
System.out.print("*");
}
System.out.println("");
}
}

First, you are skipping each 2nd iteration of the loop because you want to increase two steps at once. You can do this by changing the "i++" in your loop to "i += 2" and "i--" to "i -= 2", that will have the same effect and allows you to remove the if inside both loops.
Another improvement would be using a single outer loop and figuring out whether the inner loop should be increasing or decreasing the amount of asterisks. Maybe you can come up with an equation that gives you the amount of asterisks based on the value of i? (I didn't want to solve it completely so you have some exercise left, just comment if you want a full solution)
Updated with a solution that might be considered elegant as you can change the height of the triangle and there is no repetition:
int height = 5;
for (int i = 1; i <= 2 * height; i += 2) {
int numAsterisks;
if (i <= height) {
numAsterisks = i;
} else {
numAsterisks = 2 * height - i;
}
for (int j = 0; j < numAsterisks; j++) {
System.out.print("*");
}
System.out.println();
}

What about the following?
public void printTriangle(int size) {
int half = size / 2;
for (int i = 0; i < size; i++) {
int stars = 1 + 2 * (i <= half ? i : size - 1 - i);
char[] a = new char[stars];
Arrays.fill(a, '*');
System.out.println(new String(a));
}
}
Or just a bit more optimized:
public void printTriangle(int size) {
int half = size / 2;
char[] a = new char[size];
Arrays.fill(a, '*');
for (int i = 0; i < size; i++) {
int stars = 1 + 2 * (i <= half ? i : size - 1 - i);
System.out.println(new String(a, 0, stars));
}
}

for(int i = 0; i < 7; i++) {
for(int j = 0; j < i; j++) {
print("*");
}
print("\n");
}
This can be another solution to print a regular right triangle...

Here's a different way of looking at the problem. By using an integer array, I can solve lots of shape drawing problems by changing the values in the array.
When solving more difficult problems, you would use model classes instead of simple integers. The idea, however, is the same.
Here's the output.
*
***
*****
***
*
And here's the code:
public class Triangle {
public static void main(String[] args) {
int[] heights = {1, 3, 5, 3, 1};
for (int i = 0; i < heights.length; i++) {
for (int j = 0; j < heights[i]; j++) {
System.out.print("*");
}
System.out.println("");
}
}
}

How about...
int width = 5;
for (int i = 1; i <= width; i+=2){
System.out.println(String.format("%"+i+"s", "").replaceAll(" ", "*"));
}
for (int i = width-2; i > 0; i-=2){
System.out.println(String.format("%"+i+"s", "").replaceAll(" ", "*"));
}
Or, even better yet...
int width = 7;
double half = width / 2
for (int i = 0; i < width; i++){
System.out.println(String.format("%"+((i < half ? i : (width-i-1))*2+1)+"s", "").replaceAll(" ", "*"));
}
Gives
*
***
*****
***
*