More recursive method to print Pascal's triangle

Question

I'll try to use a recursive method to print pascals triangle to the standard output. I started by making an iterative method to get an idea of ​​how I wanted the method to work. See the code below.

/**
 * Print Pascal's triangle with PrintOut.
 *
 * @param n The amount of rows in total
 */
public static void printPascal(int n) {
    for (int i = 0; i < n; i++) {
        System.out.format("%" + (n - i) * 3 + "s", "");
        for (int j = 0; j <= i; j++) {
            System.out.format("% 6d", binom(i, j));
        }
        System.out.println();
    }
}

Javadoc and the signature of binom

/**
 * Method which calculates the values in Pascal's triangle.
 *
 * @param n The row of "the place"
 * @param k The column of "the place"
 * @return A value on "the place" from the triangle
 */
public static int binom(int n, int k)

Then i began to work on the recursive method. I can not use any class variable for printing - so I can not use a vector. I can not have any object, the class the methods are in, the two methods and main are the only methods I can implement. The biggest problem is that I can not save the variables that binom should use because they reset after each iteration. Now I have this code for printPascal:

if (n < 0) {
    return;
}
printPascal(n - 1);
for (int k = 0; k <= n; k++) {
    System.out.format("%6d", binom(n, k));
}
System.out.println();

Is there a way to make the method above more recursive - is there a way to take away the for-loop?

Answer 1

I hope this helps?

public class PascalTriangle {
    public static void main(String[] args) {
        printPascal(5);
    }

    private static void printPascal(int i) {
        auxPrintPascal(0, i);
    }

    private static void auxPrintPascal(int row, int numOfRows) {
        if (row > numOfRows) {
            return;
        }
        printPascalTriangleRow(row, 0);
        System.out.println();
        auxPrintPascal(row + 1, numOfRows);
    }

    private static void printPascalTriangleRow(int row, int col) {
        if (col > row) {
            return;
        }
        System.out.print(binomial(row, col) + " ");
        printPascalTriangleRow(row, col + 1);
    }

    private static long binomial(int n, int k) {
        if (k > n - k)
            k = n - k;

        long b = 1;
        for (int i = 1, m = n; i <= k; i++, m--)
            b = b * m / i;
        return b;
    }
}

If you insist, this should work?

private static void sillyPrintPascal(int row, int col, int numOFRows) {
    if (row > numOFRows) {
        return;
    }
    if (col > row) {
        return;
    }
    System.out.print(binomial(row, col) + " ");
    if (col == row) {
        System.out.println();
        sillyPrintPascal(row + 1, 0, numOFRows);
    } else {
        sillyPrintPascal(row, col + 1, numOFRows);
    }
}