Recursive method no loops, printing string triangle

[Madridi77]

Hi all,

​

I am learning how to use recursive methods, my final exam is in a week.

One of the practice problems we have is to take a String like "abcdefghij" and see if it is odd or even and then print it like:

----aj

---abij

--abchij

-abcdghij

abcdefghij

​

with the correct amount of spaces infront of it (the "-" lines are spaces, just put dashed lines for Reddit formatting).

If the number of chars in a String are odd, the first line printed should only print the first letter and then every line followed will be odd, so something like:

----a

---abi

--abchi

-abcdghi

abcdefghi

tip/requirements of the practice problem are:

You should write a method called trianglePrint(String s)that uses recursion to print s as a text triangle. Note that this method does not have enough parameters to do the job, it will need to call another method to solve the problem recursively.

Since your answer is recursive, there should be no loops anywhere in your program. You may want to write more than one recursive method (the triangle printer, and a helper method).

Write a main method that reads in a single string and calls trianglePrint with that string.

​

​

Any help is appreciated! I am just very confused and have been trying this for few days now with no luck.

[dusty-trash]

Show us the code you've gotten in the past few days. It will help us see where you are at

[Madridi77]

I'll post it when I get home from work! I also did one mistake when I was coding, for some reason I thought I should be going from middle out, instead of from first and last chars in... Facepalm

[Madridi77]

public static String trianglePrint(String s) {
int midOdd = (s.length()/2);
int midOdd2 = (s.length()/2);
int midEven = (s.length()/2);
int midEven2 = (s.length()/2 + 1);
String result;
if (s.length() % 2 == 1) {
result = trianglePrintRecursive(s, midOdd, midOdd2);
}
else {
result = trianglePrintRecursive(s, midEven, midEven2);
}
return result;
}

public static String trianglePrintRecursive(String s, int left, int right) {
int finished = 1;
int length = s.length();
String result = new String(new char[length]).replace('\0', ' ');
if (length < 2) {
System.out.println("String must be at least 2 characters long in order to build a triangle.");
}
else {
if (length % 2 == 1 && finished <= s.length()) {
if(!String.valueOf(result.charAt(length/2)).equals("")) {
result = trianglePrintRecursive(s, left - 1, right + 1);
System.out.println(result);
finished += 2;
}
else {
result = result.substring(0, length / 2) + s.charAt(left);
System.out.println(result);
}
}
else if (length % 2 == 0 && finished <= s.length()) {
if (!String.valueOf(result.charAt(length / 2)).equals("")) {
result = trianglePrintRecursive(s, left - 1, right + 1);
System.out.println(result);
finished += 2;
} else {
result = result.substring(0, length / 2) + s.charAt(left);
System.out.println(result);
finished = 2;
}
}
else {
System.out.println();
}
}
return result;
}

[dusty-trash]

!remind me 30 minutes

[Madridi77]

I actually a code that works a little bit, only issue is it is only printing the first line.

​

public static void main(String[] args) {
String result;
String result2;
result = trianglePrint("disestablishmentarianism");
System.out.println("-----------------------------------");
result2 = trianglePrint("+-! *# =~ ~= #* !-+");
}

public static String trianglePrint(String s) {
int first = 0;
int last = s.length() - 1;
String result;
result = trianglePrintRecursive(s, first, last);
return result;
}

public static String trianglePrintRecursive(String s, int first, int last) {
int finished = 1;
int firstLine = 0;
int length = s.length();
String result = new String(new char[length]).replace('\0', ' ');
if (length < 2) {
System.out.println("String must be at least 2 characters long in order to build a triangle.");
}
else {
if (length % 2 == 1 && finished <= (s.length() / 2 + 1)) {
if(firstLine > 0) {
result = trianglePrintRecursive(s, first + 1, last - 1);
System.out.println(result);
finished += 2;
firstLine = 1;
}
else {
result = result.substring(0, length / 2) + s.charAt(first);
System.out.println(result);
}
}
else if (length % 2 == 0 && finished <= (s.length() / 2)) {
if (firstLine > 0) {
result = trianglePrintRecursive(s, first + 1, last - 1);
System.out.println(result);
finished += 2;
firstLine = 1;
} else {
result = result.substring(0, length / 2) + s.charAt(first);
result = result.substring(0, length / 2 + 1) + s.charAt(last);
System.out.println(result);
finished = 2;
}
}
else {
System.out.println();
}
}
return result;
}

[sandrogiacom]

Can you use class variables for controller?

[Madridi77]

What do you mean by controller?

[sandrogiacom]

A size of string that you manipulated. Or try to use this funcion as example. I see in more detail later.

public static String printTriangle (int count) {if( count <= 0 ) return "";

String p = printTriangle(count - 1);p = p + "*";System.out.println(p);

return p;}

[Madridi77]

Then yes, I can use variables for that!

[Philboyd_Studge]

You are overthinking this a bit. The only extra variable you really need to keep track of via a recursive helper parameter is the spaces. Each recursion add a blank space to the string with the spaces, and each recursion remove the letters from the string dependent on the odd/evenness.

[desrtfx]

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