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Posted on 2011-09-19
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Hi Friends,
Recently I saw one article regarding list implementations i.e  For LinkedList get is O(n) and
For ArrayList get is O(1) please explain the difference between them?
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Question by:PrakashVarma
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for_yan earned 2000 total points
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In LinkedList in order to get to element number n you need to traverse other elements - therefore the longer the list the more time t takes to get to element with certain number
This means O(m) - the time is proportional to the number of elements

In the ArrayList you just calculate where is your element with the number n and immediately go there - therefore the
time to get to certain element does not dpend on the length of the list - this means O(1) - the time is constant - indpendent of the numebr of elements

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Expert Comment

ID: 36558870

see
http://en.wikipedia.org/wiki/Time_complexity

about time complexity of algrorithms in computation
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for_yan earned 2000 total points
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Imagine say list of elements where each element tells you where is the next element - the longer will be such lsit the more time on average you would need
to get to sertain element

On the other hand imagine list of elements which has an index which tells where is the location of each elemet - then by number of element
you can calculate where is the address of particular element and no matter how long is the list this calculation will take the same time

This is analogy which corresponds to LinkedLst and ArrayList

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for_yan earned 2000 total points
ID: 36558903
On the other hand if you want to insert element into certain position - in case of ArrayList you'll have to
shift all elements say upwards to make the space for the new element - so the longer list you have it will take longer time

In LinkedList you just need to chenge the pointers of two neighboring elements and the time it takes to insert
element into any pposition will be the same.

Therefore if you have really long lists where most of the time you need to insert new elements
then you want to use linkedlist . If you have long lists and you populate it just once and then you want
mostly to read elements - then ArrayList would be more efficient.

Of course if lists are short - then all of it is not so much relevant, but when you get in many thousads of elements
then it becomes significant

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