Create a triangle out of stars using only recursion

Question

I need to to write a method that is called like printTriangle(5);. We need to create an iterative method and a recursive method (without ANY iteration). The out

Answer 1

You can do it like this:

The method gets the number of stars as a parameter. Let's call it n.

Then it:

1. calls itself recursively with n-1.

2. prints a line with n stars.

Make sure to do nothing if n == 0.

Answer 2

I think this should work... untested off the top of my head.

public void printTriangle(int count)
{    
    if (count == 0) return;
    printTriangle(count - 1);
    for (int x = 1; x <= count; x++) { 
        System.out.print("*"); 
    }
    System.out.print("\n"); 
}

Answer 3

    void trianglePrint(int rows){
            int static currentRow = 1;
            int static currentStar = 1;

            // enter new line in this condition
            // (star > currentrow)  

            if (currentStar > currentRow ){
                currentStar = 1;
                currentRow++;
                cout << endl;
            }

            if (currentRow > rows){
                return; // finish
            }

            cout << "*";
            currentStar++;

            trianglePrint(rows);
        }

Answer 4

You can also do it with a single (not so elegant) recursion,as follows:

public static void printTriangle (int leftInLine, int currLineSize, int leftLinesCount) {
    if (leftLinesCount == 0)
        return;
    if (leftInLine == 0){ //Completed current line?
        System.out.println();
        printTriangle(currLineSize+1, currLineSize+1, leftLinesCount-1);
    }else{
        System.out.print("*");
        printTriangle(leftInLine-1,currLineSize,leftLinesCount);
    }
}

public static void printTriangle(int size){
    printTriangle(1, 1, size);
}

The idea is that the method params represent the complete drawing state.

Note that size must be greater than 0.

Answer 5

package playground.tests;

import junit.framework.TestCase;

public class PrintTriangleTest extends TestCase {
    public void testPrintTriangle() throws Exception {
        assertEquals("*\n**\n***\n****\n*****\n", printTriangleRecursive(5, 0, 0));
    }

    private String printTriangleRecursive(int count, int line, int character) {
        if (line == count)
            return "";
        if (character > line)
            return "\n" + printTriangleRecursive(count, line + 1, 0);
        return "*" + printTriangleRecursive(count, line, character + 1);
    }

}

Answer 6

Example in python (just for the sake of prototyping, but I hope the idea gets through):

#!/usr/bin/env python

def printTriangle(n):
    if n > 1:
        printTriangle(n - 1)
    # now that we reached 1, we can start printing out the stars 
    # as we climb out the stack ...
    print '*' * n

if __name__ == '__main__':
    printTriangle(5)

Output looks like this:

$ python 2717111.py
*
**
***
****
*****