How to Ensure Order in LRStruct with addInOrder Method?

[MFlood7356]

1. Define this method so that it adds the Strings in inputto an initially empty LRStruct<String> so that they appearin the same order. Example: if input contains "a", "b" and "c", in that order, the returned list must contain "a", "b" and "c", in that order.

LRStruct Class: http://www.cs.rice.edu/~mgricken/research/a4obj1st/tchjava/Rice_MBS/RiceMBS.student/docs/lrs/LRStruct.html

Test:

@Test
	public void testABC() {
		_input.add("a");
		_input.add("b");
		_input.add("c");
		LRStruct<String> answer = _fwl.addInOrder(_input);
		String expected = "(a b c)";
		String actual = answer.toString();
		assertTrue("I thought answer would be "+expected+" but it was "+actual, expected.equals(actual));
	}

2. Here's my attempt at the method addInOrder. All I'm getting is the string c to add to the LRStruct. Not sure why my if statement isn't working correctly.

public LRStruct<String> addInOrder(List<String> input) {
	
		LRStruct<String> lrstruct = new LRStruct<String>();
		int counter = 2;
		
		if(counter>=0){
			lrstruct.insertFront(input.get(counter));
			counter--;
		}
		
		return lrstruct;
	}

 

[JaWiB]

I think what you're looking for is a loop. I.e.:

int counter = 2;

if(counter>=0){
			lrstruct.insertFront(input.get(counter));
			counter--;
		}

will do the exact same thing as

lrstruct.insertFront(input.get(2));

 

[MFlood7356]

Okay I understand that but that's the exact same thing I wrote. That's not helping me.

 

[JaWiB]

You need a loop

Doesn't Java have while loops, or for loops? Or for-each loops?

 

[DeeNos]

Your attempt at the method addInOrder is close, but there are a few issues that need to be addressed.

Firstly, your counter variable is starting at 2 and decreasing by 1 each time, so it will only go through the loop once. You need to start the counter at the size of the input list and decrease it by 1 each time.

Secondly, your if statement is only checking if the counter is greater than or equal to 0, which will always be true. You need to check if the counter is greater than or equal to 0 AND less than the size of the input list.

Lastly, your insertFront() method is only adding the last element of the input list to the LRStruct. You need to use a loop to add each element in the input list to the LRStruct.

Here is a revised version of your method that should work correctly:

public LRStruct<String> addInOrder(List<String> input) {

LRStruct<String> lrstruct = new LRStruct<String>();
int counter = input.size()-1; //start counter at size of input list

while(counter >= 0){ //check if counter is greater than or equal to 0 AND less than size of input list
lrstruct.insertFront(input.get(counter)); //add element to front of LRStruct
counter--; //decrease counter by 1
}

return lrstruct;
}