CODEWITHSUNDEEP
javaalgorithmlistcollectionslinked-list
Cratylus
Cratylus

Reputation: 54094

Best way to reverse a java.util.LinkedList (in place if possible)

I want to reverse a java.util.LinkedList<Integer> using the available methods.
Looking in the methods provided and the Iterators I couldn't see an option other than the following: 

int i = list.size();  
int pos = 0;  
while(i-- > 1){  
     Integer n = list.removeLast();  
     list.add(pos++, n);          
}

But surely there must be a better way. I mean it is not a good idea to modify a list outside of an iterator, but I couldn't see how I could use one here without having to create a new list.
Is there a better way?

Upvotes: 7

Views: 8102

Answers (3)

Joeri Hendrickx
Joeri Hendrickx

Reputation: 17445

There's an api method for that.

Collections.reverse(yourList);

See http://docs.oracle.com/javase/1.4.2/docs/api/java/util/Collections.html#reverse%28java.util.List%29.

If for some reason you want to do it yourself, this seems the best way:

List<T> reversed = new LinkedList<T>();
while(!yourList.isEmpty()) reversed.add(yourList.removeLast());

Upvotes: 3

tanyehzheng
tanyehzheng

Reputation: 2221

see java.util.Collections.reverse(List list)

Upvotes: 2

ehanoc
ehanoc

Reputation: 2217

Use import java.util.Collections;

Collections.reverse(list);

Upvotes: 20

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