Java Print certain pattern using for loop

Question

below are my code can anyone help me i stuck at the * part

i want the output like this

... and so on

    for (int i = 1; i <= l; i++) {
        for (int j = 1; j <= l - i; j++)
            System.out.print(" ");

        for (int j = 1; j <= (2 * i - 1); j++) {
            if((l-j) < l-i){
            // here System.out.print("*");
            }
            else
                System.out.print(l - j);

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

What have you tried? What isn't working? Are we supposed to run your code to determine what's wrong? — Falmarri
– Falmarri, Commented Dec 15, 2010 at 15:04
@org Nah, I often find the need at work to output triangles of numbers :) — Michael Mrozek
– Michael Mrozek, Commented Dec 15, 2010 at 15:04
@Falmarri I'm guessing he's tried the code snippet he posted, and he's having problems on the line commented // here ... — Michael Mrozek
– Michael Mrozek, Commented Dec 15, 2010 at 15:06

Michael Mrozek · Accepted Answer · 2010-12-15 15:18:36Z

1

I ended up rewriting it; I couldn't figure out a concise constant for the print you were missing. If you loop i from 0 to l (inclusive), you can do:

Spaces

The last line (i = l) has 0 spaces, so each line has l-i spaces:

for(int j = 0; j < l-i; j++)
    System.out.print(" ");

Left/Center

Every line starts at l, and you want to count down till you reach the center; since the current line has l-i spaces and the center is at l+1 (since I included the line with a 0 center), which is i+1 away, you need to output through l-i inclusive

for(int j = l; j >= l-i; j--)
    System.out.print(j);

Right

The same loop as above, but reversed. Starts 1 higher because the center is already handled above and you don't want to output it again

for(int j = l-i+1; j <= l; j++)
    System.out.print(j);

answered Dec 15, 2010 at 15:18

Michael Mrozek

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Comments

jon_darkstar · Accepted Answer · 2010-12-15 15:14:20Z

0

I'd rework a little more than just that one line

    for (int j = 1; j <= (2 * i - 1); j++) {
        if((l-j) < l-i){
        // here System.out.print("*");
        }
        else
            System.out.print(l - j);

To...

for(int j = 1; j < i; j++)
     System.out.print(10-j);

System.out.println(10-i);

for(int j = 1; j < i; j++)
     System.out.print(10-i+j);

answered Dec 15, 2010 at 15:14

jon_darkstar

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Comments

Hiep Ho · Accepted Answer · 2010-12-15 16:30:34Z

This is completed program. I used "divide and conquer" method (basically the same idea as of Michael Mrozek), and use method to make it extreme-easy-to-understand program . Hope this will help.

public class PatternPrinter {
public static void main(String[] args) {
    printAllRows(9, 5);
}

public static void printAllRows(int max, int numOfRows) {
    for (int i = 1; i <= numOfRows; i++) {
        printRow(numOfRows - i, max, i);
        System.out.print("\n");
    }
}

public static void printRow(int numOfSpaces, int max, int num) {
    printSpaces(numOfSpaces);
    printLeftAndCenterPart(max, num);
    printRightPart(max, num - 1);
}

public static void printRightPart(int max, int num) {
    while(num > 0) {
        System.out.print(max - num + 1);
        num--;
    }
}

public static void printLeftAndCenterPart(int max, int num) {
    while(num > 0) {
        System.out.print(max--);
        num--;
    }
}

public static void printSpaces(int numOfSpaces) {
    while(numOfSpaces > 0) {
        System.out.print(" ");
        numOfSpaces--;
    }
}

}

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Java Print certain pattern using for loop

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