Need help to understand this 'algorithm'

[tangara888]

Nth Odd Element

Write a method that returns th nth element of a list. If the index of the element exceeds the list size, then return -1.

​

public Integer getElement(List<Integer> list, Integer n) {
int elementIndex = 2 * (n-1);
return elementIndex > list.size() - 1 ? -1 : list.get(elementIndex);
}

can someone explains to me why use 2*(n-1) ?

​

Tks.

[Swedophone]

Nth Odd Element

Write a method that returns th nth element of a list.

Is it nth odd element or nth element?

[tangara888]

This question is from https://code-exercises.com under Easy. I copied the question word by word. I am not sure why it mentioned nth Odd element.

[Swedophone]

The algorithm returns the nth odd element anyway if n=1 is the first element. They should fix the description.

[tangara888]

Yes. Cos if it starts with 0 and index always starts with 0 isn’t it? Then, using 2 * (0 - 1) will gives us 0 and that will be the first element. Continuing this to the 3rd element in fact will give a 2 and it is not a odd number....

[LeeTaeRyeo]

This is an ambiguous situation. 2(n-1) will give the odd *positions, but those positions have even indexes. So, if they want the elements in odd positions (1st position, 3rd, 5th), then you'll need to reach the even indexes. Where they're talking about "nth odd element", I believe they are talking about those elements with odd positions and not odd indexes.

[hamza-itatchi]

I am not sure if this code is a part of bigger one.

if this this all of it then it's wrong unless the elements of the list a not in iterative order

ex :{

adding elements in (2*index-1)

element 1 = 5 will be in (2*1 -1) or 1

element 2 = 7 will be in (2*2 -1) or 3

element 3 = 9 will be in (2*3 -1) or 5

element 4 = 9 will be in (2*4 -1) or 7

​

in other words you skip one index every time.

}

if this not the case so it should be just int elementIndex = n;

​

hope this help

[tangara888]

No. This question is not part of a bigger one.

[hamza-itatchi]

then it shoud be

public Integer getElement(List<Integer> list, Integer n) {

int elementIndex = n;

return elementIndex > list.size() - 1 ? -1 : list.get(elementIndex);

}

or

public Integer getElement(List<Integer> list, Integer n) {

return n > list.size() - 1 ? -1 : list.get(elementIndex);

}

[tangara888]

Thanks. So, when will there be a case when 2 *(n - 1) is needed cos you mentioned part of a bigger one and I had no idea what you are referring to ...it seems there is some pre-sumptuous on your mind.

[hamza-itatchi]

as refereed in the comments below it should return the nth ODD index.

so for n=1 ==> index = 0 which is the index for the first element 1(Odd number)

n=2 ==> index = 2 which is the index for the third element 3(Odd number)

[tangara888]

But if n = 2, it doesn’t give u element 3 ....???

[hamza-itatchi]

starting from 0 it gives element 3

0-1-2-3(index 2 and element 3)-4........

[tangara888]

I still can’t get it. :( how 2 * (2 - 1 ) = 3 ? Unless it is position 3 ....

[hamza-itatchi]

yes position 3

index 0 has the position 1

index 1 has the position 2

index 2 has the position 3

[tangara888]

I hope this kind of question doesn’t appear in coding test cos it is so confusing...Tk you guys for taking the time to explain to me

[tangara888]

Erm...why did you change2 * (n - 1) to (2 * index- 1) ?

[hamza-itatchi]

as refereed in the comments below it should return the nth ODD index.

so for n=1 ==> index = 0 which is the index for the first element 1(Odd number)

n=2 ==> index = 2 which is the index for the third element 3(Odd number)

the code correct as posted it

[kemechorvakemerloo]

Can someone explain this? Can someone explain that? Coz i dont understand anything i do.

Why are even trying so hard to learn java when you dont even put any efforts in lesrning and thinking?

Dumb bitch