Pascal's triangle 2d array - formatting printed output

Question

I have a small assignment where I have to use a 2d array to produce Pascal's triangle. Here is my code, and it works. There is an extra credit opportunity if I display the triangle like so:

_{(source: daugerresearch.com)}

However, my spacing is not formatted like that. it simply displays the numbers all lined up on the left. its hard to describe but if you run it you will see what I mean.

Here is my code:

public class Pascal {
    public static final int ROW = 16;
    public static void main(String[] args) {
        int[][] pascal = new int[ROW + 1][];
        pascal[1] = new int[1 + 2];
        pascal[1][1] = 1;
        for (int i = 2; i <= ROW; i++) {
            pascal[i] = new int[i + 2];
            for (int j = 1; j < pascal[i].length - 1; j++) {
                pascal[i][j] = pascal[i - 1][j - 1] + pascal[i - 1][j];
            }
        }
        for (int i = 1; i <= ROW; i++) {
            for (int j = 1; j < pascal[i].length - 1; j++) {
                System.out.print(pascal[i][j] + " ");
            }
            System.out.println();
        }
    }
}

If someone could help me figure out how to add the correct spacing to my program to produce the output desired in the picture, that would be great. I know I need to put a System.out.print(" ") somewhere. I just dont know where.

http://stackoverflow.com/questions/2709993/how-to-center-string-output-using-printf-and-variable-width-java — Marek Sebera, Jan 20 '12 at 00:17

score 7 · Accepted Answer · edited Jun 26 '21 at 03:15

Here I had modified your code, it prints wonderfully for ROW size till 13, because of the limitation of my console window:

import java.util.*;

public class Pascal {
    public static final int ROW = 12;
    private static int max = 0;

    public static void main(String[] args) {
        int[][] pascal = new int[ROW + 1][];
        pascal[1] = new int[1 + 2];
        pascal[1][1] = 1;
        for (int i = 2; i <= ROW; i++) {
            pascal[i] = new int[i + 2];
            for (int j = 1; j < pascal[i].length - 1; j++) {
                pascal[i][j] = pascal[i - 1][j - 1] + pascal[i - 1][j];
                String str = Integer.toString(pascal[i][j]);
                int len = str.length();
                if (len > max)
                    max = len;
            }
        }

        for (int i = 1; i <= ROW; i++) {
            for (int k = ROW; k > i; k--)
                System.out.format("%-" + max + "s", " ");
            for (int j = 1; j < pascal[i].length - 1; j++)
                System.out.format("%-" + (max + max) + "s", pascal[i][j]);
            System.out.println();
        }
    }
}

Output:

                                 1     
                              1     1     
                           1     2     1     
                        1     3     3     1     
                     1     4     6     4     1     
                  1     5     10    10    5     1     
               1     6     15    20    15    6     1     
            1     7     21    35    35    21    7     1     
         1     8     28    56    70    56    28    8     1     
      1     9     36    84    126   126   84    36    9     1     
   1     10    45    120   210   252   210   120   45    10    1     
1     11    55    165   330   462   462   330   165   55    11    1

score 5 · Answer 2 · answered Jan 20 '12 at 00:24

You're encountering spacing issues because you need to add whitespace to certain numbers to accommodate space that larger numbers occupy. First determine what the largest number you plan to print is (programmatically). Then determine the number of digits in that number log(n). You can then use this number to print whitespace for numbers that have less digits than your largest number to make your printing look nicer.

score 2 · Answer 3 · 2021-02-16T18:59:29.213

You can build a Pascal's triangle in the upper left corner of a 2d array that looks like this:

 1  1  1  1  1  1  1  1  1  1
 1  2  3  4  5  6  7  8  9
 1  3  6 10 15 21 28 36
 1  4 10 20 35 56 84
 1  5 15 35 70 126
 1  6 21 56 126
 1  7 28 84
 1  8 36
 1  9
 1

Two nested streams: over the rows and then over the columns. Elements of the first row and column are equal to one, all other elements are the sum of the previous element in the row and column.

int n = 10;
// an array of 'n' rows
int[][] arr = new int[n][];
// iterate over the rows of the array
IntStream.range(0, n)
        // a row of 'n-i' elements
        .peek(i -> arr[i] = new int[n - i])
        // iterate over the elements of the row
        .forEach(i -> IntStream.range(0, n - i).forEach(j -> {
            if (i == 0 || j == 0)
                // elements of the first row
                // and column are equal to one
                arr[i][j] = 1;
            else
                // all other elements are the sum of the
                // previous element in the row and column
                arr[i][j] = arr[i][j - 1] + arr[i - 1][j];
        }));

// formatted output
Arrays.stream(arr)
        .map(row -> Arrays.stream(row)
                // format as a two-digit number
                .mapToObj(i -> String.format("%2d", i))
                .collect(Collectors.joining(" ")))
        .forEach(System.out::println);

"%2d" - format as a two-digit number, when n=10,

"%4d" - format as a four-digit number, when n=16, and so on.

score 0 · Answer 4 · edited Jun 27 '21 at 04:08

You can also refer to the below code.

public class Pascal {
    public static final int ROW = 16;

    static long factorial(int ROW) {
        long f;
        for (f = 1; ROW > 1; ROW--) {
            f *= ROW;
        }
        return f;
    }

    static long patt(int ROW, int r) {
        return factorial(ROW) / (factorial(ROW - r) * factorial(r));
    }

    public static void main(String args[]) {
        System.out.println();
        int i, j;
        for (i = 0; i <= ROW; i++) {
            for (j = 0; j <= ROW - i; j++) {
                System.out.print(" ");
            }
            for (j = 0; j <= i; j++) {
                System.out.print(" " + patt(i, j));
            }
            System.out.println();
        }
    }
}

Output:

                  1
                 1 1
                1 2 1
               1 3 3 1
              1 4 6 4 1
             1 5 10 10 5 1
            1 6 15 20 15 6 1
           1 7 21 35 35 21 7 1
          1 8 28 56 70 56 28 8 1
         1 9 36 84 126 126 84 36 9 1
        1 10 45 120 210 252 210 120 45 10 1
       1 11 55 165 330 462 462 330 165 55 11 1
      1 12 66 220 495 792 924 792 495 220 66 12 1
     1 13 78 286 715 1287 1716 1716 1287 715 286 78 13 1
    1 14 91 364 1001 2002 3003 3432 3003 2002 1001 364 91 14 1
   1 15 105 455 1365 3003 5005 6435 6435 5005 3003 1365 455 105 15 1
  1 16 120 560 1820 4368 8008 11440 12870 11440 8008 4368 1820 560 120 16 1

score 0 · Answer 5 · 2021-07-03T18:01:58.173

With respect to this previous answer, you can output a formatted triangle in the upper left corner using two nested enhanced for loops.

    1    1    1    1    1    1    1    1    1    1    1    1    1    1
    1    2    3    4    5    6    7    8    9   10   11   12   13
    1    3    6   10   15   21   28   36   45   55   66   78
    1    4   10   20   35   56   84  120  165  220  286
    1    5   15   35   70  126  210  330  495  715
    1    6   21   56  126  252  462  792 1287
    1    7   28   84  210  462  924 1716
    1    8   36  120  330  792 1716
    1    9   45  165  495 1287
    1   10   55  220  715
    1   11   66  286
    1   12   78
    1   13
    1

Try it online!

int n = 14;
// an array of 'n' rows
int[][] arr = new int[n][];
// iterate over the rows of the array
for (int i = 0; i < n; i++) {
    // a row of 'n-i' elements
    arr[i] = new int[n - i];
    // iterate over the elements of the row
    for (int j = 0; j < n - i; j++) {
        if (i == 0 || j == 0) {
            // elements of the first row
            // and column are equal to one
            arr[i][j] = 1;
        } else {
            // all other elements are the sum of the
            // previous element in the row and column
            arr[i][j] = arr[i][j - 1] + arr[i - 1][j];
        }
    }
}

// formatted output
for (int[] row : arr) {
    for (int i : row)
        // format as a four-digit number with one
        // additional whitespace at the beginning
        System.out.printf(" %4d", i);
    System.out.println();
}

Pascal's triangle 2d array - formatting printed output

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