AVL and Red black trees are both self-balancing except Red and black color in the nodes. What's the main reason for choosing Red black trees instead of AVL trees? What are the applications of Red black trees?
What's the main reason for choosing Red black trees instead of AVL trees?
Both red-black trees and AVL trees are the most commonly used balanced binary search trees and they support insertion, deletion and look-up in guaranteed O(logN) time. However, there are following points of comparison between the two:
- AVL trees are more rigidly balanced and hence provide faster look-ups. Thus for a look-up intensive task use an AVL tree.
- For an insert intensive tasks, use a Red-Black tree.
- AVL trees store the balance factor at each node. This takes
O(N)extra space. However, if we know that the keys that will be inserted in the tree will always be greater than zero, we can use the sign bit of the keys to store the colour information of a red-black tree. Thus, in such cases red-black tree takes no extra space.
What are the application of Red black tree?
Red-black trees are more general purpose. They do relatively well on add, remove, and look-up but AVL trees have faster look-ups at the cost of slower add/remove. Red-black tree is used in the following:
- Java:
java.util.TreeMap,java.util.TreeSet - C++ STL (in most implementations): map, multimap, multiset
- Linux kernel: completely fair scheduler, linux/rbtree.h
Try reading this article
It offers some good insights on differences, similarities, performance, etc.
Here's a quote from the article:
RB-Trees are, as well as AVL trees, self-balancing. Both of them provide O(log n) lookup and insertion performance.
The difference is that RB-Trees guarantee O(1) rotations per insert operation. That is what actually costs performance in real implementations.
Simplified, RB-Trees gain this advantage from conceptually being 2-3 trees without carrying around the overhead of dynamic node structures. Physically RB-Trees are implemented as binary trees, the red/black-flags simulate 2-3 behaviour
As far as my own understanding goes, AVL trees and RB trees are not very far off in terms of performance. An RB tree is simply a variant of a B-tree and balancing is implemented differently than an AVL tree.
Our understanding of the differences in performance has improved over the years and now the main reason to use red-black trees over AVL would be not having access to a good AVL implementation since they are slightly less common perhaps because they are not covered in CLRS.
Both trees are now considered forms of rank-balanced trees but red-black trees are consistently slower by about 20% in real world tests. Or even 30-40% slower when sequential data is inserted.
So people who have studied red-black trees but not AVL trees tend to choose red-black trees. The primary uses for red-black trees are detailed on the Wikipedia entry for them.
Other answers here sum up the pros & cons of RB and AVL trees well, but I found this difference particularly interesting:
AVL trees do not support constant amortized update cost [but red-black trees do]
Source: Mehlhorn & Sanders (2008) (section 7.4)
So, while both RB and AVL trees guarantee O(log(N)) worst-case time for lookup, insert and delete, restoring the AVL/RB property after inserting or deleting a node can be done in O(1) amortized time for red-black trees.
Programmers generally don't like to dynamically allocate memory. The problem with the avl tree is that for "n" elements you need atleast log2(log2(n))...(height->log2(n)) bits to store the height of the tree! So when you are handling enormous data you cannot be sure of how many bits to allot for storing height at each node.
For instance if you use 4 bytes int (32 bits) for storing height. Maximum height can be : 2^32 and hence Maximum number of elements you can store in the tree is 2^(2^32) --(seems to be very big but in this age of data nothing is too big I guess). And hence if you over shoot this limit you have to dynamically allocate more space for storing height.
This is an answer suggested by a professor at my university which seemed reasonable to me! Hope I make sense.
Edits:The AVL trees are more balanced compared to Red Black Trees, but they may cause more rotations during insertion and deletion. So if your application involves many frequent insertions and deletions, then Red Black trees should be preferred. And if the insertions and deletions are less frequent and search is more frequent operation, then AVL tree should be preferred over Red Black Tree. --Source GEEKSFORGEEKS.ORG
Re-balancing of AVL tree should meet the below property. (Wiki Reference - AVL Tree)
In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property.
So this implies that the overall height of AVL tree can not go mad i.e lookups are going to be better with AVL Trees. And since additional operations(rotations) are to be made to not let the height go mad, the tree modification operations can be bit costly.
来源：https://stackoverflow.com/questions/13852870/red-black-tree-over-avl-tree