Programmatically center text output in for loop

Question

I'm trying to put out the following pattern of chars:

    x
   xxx
  xxxxx
 xxxxxxx
xxxxxxxxx

And this is what I currently have:

String y = "";
for(int i = 0; i < 10; i++)
{
      y="";
      for(int s = 0; s < i; s++)
      {
         y+= "x";
      }
      System.out.println(y);
}

This outputs

x
xx
xxx
xxxx
xxxxx
xxxxxx
xxxxxxx
xxxxxxxx

Which is an approach. I'm well aware of the fact that the target pattern increments two x each execution of the loop, and I know that I have to use blank spaces and insert them. However, I'm stuck with this really simple task.

EDIT: The task is to only use two loops. I thought of a way using three, though, but couldn't straight forwardly figure out a way to use two loops.

Welcome to Stack Overflow! It looks like you may be asking for homework help. While we have no issues with that per se, please observe these [dos and don'ts](http://meta.stackoverflow.com/questions/334822/how-do-i-ask-and-answer-homework-questions/338845#338845), and edit your question accordingly. (Even if this isn't homework, please consider the advice anyway.) — Joe C, Apr 27 '17 at 21:37
`IntStream.range(0, 10).filter(i -> i % 2 == 0) .mapToObj(i -> Stream.generate(() -> "").limit((lines - i) / 2).collect(Collectors.joining(" ")) + Stream.generate(() -> "x").limit(1 + i).collect(Collectors.joining())) .forEachOrdered(System.out::println);` — Elliott Frisch, Apr 27 '17 at 21:50
Thank you, @JoeC! However, it's not an actual homework but something I stumbled upon while checking some pivotal algorithms and functions (despite being an ordinary programmer). — John, Apr 27 '17 at 21:50

score 2 · Answer 1 · 2017-04-27T23:36:59.080

Rather than using two for loops, I used 1 for loop and 1 if statement (which is not a loop).

    String spaces = "     ";
    String word = "";
    String X = "x";
    for(int i = 10; i > 0; i--) {
        if (i%2 == 0) {
         word = spaces + X;  
         System.out.println(word);
         spaces = spaces.replaceFirst(" ","");
         X += "xx";
        }
    }

and the output is how you asked:

     x
    xxx
   xxxxx
  xxxxxxx
 xxxxxxxxx

Youcef LAIDANI · Answer 2 · 2017-04-28T11:17:56.933

1

You can solve your problem, with just one loop, you can use padLeft with String.format, here is a simple example :

public static void main(String args[]) {
    int n = 5;
    String str;
    for (int i = n; i > 0; i--) {
        str = String.format("%0" + ((n - i) * 2 + 1) + "d", 0).replace("0", "x");
        System.out.println(String.format("%1$" + ((i - 1 + str.length())) + "s", str));
    }
}

Output

    x
   xxx
  xxxxx
 xxxxxxx
xxxxxxxxx

edited Apr 28 '17 at 11:17

answered Apr 27 '17 at 21:45

Youcef LAIDANI

55,661
15
90
140

Great approach, however, I was given the task to only use TWO for loops (I edited the question just before after I noticed I had forgotten this point). Is this technically even possible? I made a similar approach with more than two loops, though. – John Apr 27 '17 at 21:47
so you want to use just two loops @John ? – Youcef LAIDANI Apr 27 '17 at 21:49
@John check my edit, you can solve your problem with just one loop ;) – Youcef LAIDANI Apr 28 '17 at 11:18

score 1 · Accepted Answer · 2017-04-27T22:01:49.670

As there are many different possible answers to this question, this is just one possible solution.

For this solution, I don't bother printing the spaces after the X's. I only print those that come before.

int baseWidth = 10;


for (int a = baseWidth ; a > 0 ; a--) {
  for (int b = 0 ; b < a - 1 ; b++) {
    System.out.print(" ");
  }

  for (int b = a - 1 ; b < baseWidth - (a - 1) ; b++) {
    System.out.print("X");
  }

  System.out.print("\n");
}

The result of the above code is as follows for baseWidth = 10:

    XX
   XXXX
  XXXXXX
 XXXXXXXX
XXXXXXXXXX

The result of the above code is as follows for baseWidth = 9:

    X
   XXX
  XXXXX
 XXXXXXX
XXXXXXXXX

Following the edit of your post, this next code snip performs the same function as the previous one, but with only two loops.

int baseWidth = 9;


for (int a = baseWidth ; a > 0 ; a--) {
  for (int b = 0 ; b < baseWidth - (a - 1) ; b++) {
    if (b < a - 1) {
      System.out.print(" ");
    }

    if (b >= a - 1 && b < baseWidth - (a - 1)) {
        System.out.print("X");
    }
  }

  System.out.print("\n");
}

jrook · Answer 4 · 2017-04-28T01:37:59.890

Just for fun, let's have a no-loops-at-all solution too:

static Stack<String> getStarryStrings (String lastString, Stack<String> result) {
    //First count the number of *'s in the string
    //From:http://stackoverflow.com/questions/275944/java-how-do-i-count-the-number-of-occurrences-of-a-char-in-a-string
    int starCount = lastString.length() - lastString.replace("*", "").length();
    if(starCount<1) return result;
    result.push(lastString);

    //Find first and last occurrences of *
    int fio = lastString.indexOf('*');
    int lio = lastString.lastIndexOf('*');

    //And replace them with white spaces
    StringBuilder nextLast = new StringBuilder(lastString);
    nextLast.replace(fio,fio+1," ");
    nextLast.replace(lio, lio + 1, " ");

    //And recurse...
    return getStarryStrings(nextLast.toString(),result);
}


public static void main(String[] args) {
    Stack<String> res = getStarryStrings("*********",new Stack<>());
    while(!res.isEmpty()) {
        System.out.println(res.pop());
    }

Displays:

    *    
   ***   
  *****  
 ******* 
*********

Note: I am certain this can be done in a more efficient way to eliminate the need for a java.util.Stack. My only criteria was not using loops. I am letting the stack to remain there to show the recursive nature of the solution. It can easily be improved to use a StringBuilder in place of a stack.

Rajeev Singh · Answer 5 · 2017-04-27T22:21:03.627

Maintain two pointer l & r which will decide from which position to which you have to print * otherwise print space. After each line decrease the l and increase r by 1, as triangle grows 1 step to left and right in each line.

Using only two loops...

int n = 5; // number of lines...
int l = n-1, r = n-1;
for(int i = 0; i < n; i++) {
    for(int s = 0; s < 2*n; s++) {
        if(s >= l && s<= r)
            System.out.print("*");
        else
            System.out.print(" ");
    }
    System.out.println();
    l--; r++;
}

Output:

    *
   ***
  *****
 *******
*********

Ishan Dave · Answer 6 · 2017-04-27T22:38:01.940

0

Two Loops.

char[] s = "           ".toCharArray();
int start = 5;
int end = 5;
for (int i = 0; i < 5; i++) {
    for (int j = start; j <= end; j++) {
        s[j] = 'x';

    }       
    start--;
    end++;
    System.out.println(s);
}

One loop

char[] s = "           ".toCharArray();
int start = 4;
int end = 5;
for (int i = 0; i < 5; i++) {
    Arrays.fill(s, start, end, 'x');//Remembering importing Arrays class
    start--;
    end++;
    System.out.println(s);
}

edited Apr 27 '17 at 22:38

answered Apr 27 '17 at 22:31

Ishan Dave

121
5

If you have any doubt with the code just reply here in the comment section. – Ishan Dave Apr 27 '17 at 22:52

Yahya · Answer 7 · 2017-04-28T06:03:29.903

You may want to have a look at this:

public class CenterText {
    public static void main(String[] args){
        centerText(10, 'X');
    }

    public static void centerText(int noOfLines, char theChar){

        final int totalNoOfChars = noOfLines * 2;
        String totalSpaces = "";
        String chars = "";

        for (int i=0; i<totalNoOfChars; i++){
            totalSpaces += " ";
        }

        for (int j=1 ; j<=totalNoOfChars; j++){
            chars+=theChar;
            if(j%2==0){
                System.out.println(totalSpaces.substring(0, noOfLines-(j/2)) + chars);
            }       
        }   
  }


}

Examples:

Input:

centerText(10, 'X');

Output:

         XX
        XXXX
       XXXXXX
      XXXXXXXX
     XXXXXXXXXX
    XXXXXXXXXXXX
   XXXXXXXXXXXXXX
  XXXXXXXXXXXXXXXX
 XXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXX

Input:

centerText(7, '#');

Output:

      ##
     ####
    ######
   ########
  ##########
 ############
##############

Programmatically center text output in for loop

7 Answers7

Examples:

Linked