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Reverse arraylist
Hi every one.... How can i reverse an arraylist in java without using any methods.... Like Collections.reverse () ; and etc...
8 odpowiedzi
+ 6
Denise Roßberg Yeah i do know that, but i am talking about the way of thinking. His way is the standard way of reversing an array, yours takes O(n) but still it is creative ^ ^
+ 5
Honestly, just use in-builts. Usually they're built by smarter people who could do it better than you could.
+ 4
You don't need a second list.
for(int i = list.size() - 1; i >= 0; i--){
//add the value to the list
list.add(list.get(i));
//remove value
list.remove(i);
}
E.g. 1 2 3 4
index = 3, value = 4
1 2 3 4 4 (add 4 & remove 4 at index 3)
-> 1 2 3 4
index = 2, value = 3
1 2 3 4 3 (add 3 & remove 3 at index 2)
-> 1 2 4 3
index = 1, value = 2
1 2 4 3 2 (add 2, remove 2 at index 1)
-> 1 4 3 2
index = 0, value = 1
1 4 3 2 1 (add 1 && remove 1 at index 0)
-> 4 3 2 1 -> done
+ 4
List reversing using variable value swap method:
https://code.sololearn.com/c3yfniOgu249/?ref=app
+ 4
Denise Roßberg UwU That's cool algorithm 😍
+ 2
You can make a new list:
Arraylist newlist = new Arraylist()
for (int i = list.size() -1 ; i >= 0; i --){
newlist.add(list.get(i));
}
But maybe there are better solutions
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Umar