Need help with a programming assignment in java using recursion, NO LOOPS!

Here are the two methods that I need to implement that I am having trouble with:

void printPattern(int n)

Precondition: n>0 Postcondition: print a pattern of n+1 lines ( 0 to n ): line i (i = 0 to n) has i stars ("*"), followed by (n-i) stripes ("-")

For example, printPattern(3) prints:

--- *-- **- *** 

hint: use a private recursive helper function, with more parameters, that does the work, e.g.:

 private void printPattern(int stars, int stripes) 

You may need another helper function...

ArrayList intersection( ArrayList AL1, ArrayList AL2)

Precondition: AL1 and AL2 are not empty, and elements in AL1 are unique, and elements in AL2 are unique, (but AL1 and AL2 can contain the same elements) Postcondition: return an ArrayList with elements that are in both AL1 and AL2, *** in the order they occur in AL1 ***, and *** leave AL1 and AL2 unchanged ***

For example:

 ArrayList AL1 = new ArrayList(); ArrayList AL2 = new ArrayList(); AL1.add("a"); AL1.add("b"); AL1.add("c"); AL2.add("b"); AL2.add("c"); AL2.add("d"); AL2.add("e"); ArrayList intersect = A3.intersection(AL1,AL2); System.out.println(AL1 + " intersect " + AL2 + " = " + intersect); prints: [a, b, c] intersect [b, c, d, e] = [b, c] 

hint: What kind of helper method would you use here?

Below is the code I have written so far, but it does not work:

public void printPattern(int n) {

if (n>0)

helperPrintPattern(0,n);

}

//Helper method for printPattern

private void helperPrintPattern(int stars, int stripes ) {

if(stars< 0){

return;

}

else{

System.out.println();

printStars(stars);

printStripes(stripes - stars);

helperPrintPattern(++stars,--stripes);

}

}

//Helper method for stars

private void printStars(int i){

if (i!=0){

System.out.println("*");

printStars(i-1);

}

}

//Helper method for stripes

private void printStripes(int j){

if (j!=0){

System.out.println("-");

printStripes(j-1);

}

}

public ArrayList intersection(ArrayList AL1, ArrayList AL2) {

ArrayList empty = new ArrayList();

if(!AL1.isEmpty() && !AL2.isEmpty()){

intersection(AL1,AL2,empty,0,AL1.size()-1,0,AL2.size()-1);

}

return empty;

}

//Intersection helper function

private ArrayList intersection(ArrayList AL1,ArrayList AL2,ArrayList result, int Findex1, int Lindex1, int Findex2, int Lindex2){

if(Findex1<=Lindex1){

if(Findex2<=Lindex2){

if(AL1.get(Findex1).equals(AL2.get(Findex2))){

result.add(AL1.get(Findex1));

}

intersection(AL1,AL2,result,Findex1,Lindex1,++Findex2,Lindex2);

}

else{

intersection(AL1,AL2,result,++Findex1,Lindex1,Findex2,Lindex2);

}

}

return result;

}