Advantages of Binary Search Trees over Hash Tables

data-structures hashtable binary-search-tree
Devoted picture Devoted · Nov 8, 2010 · Viewed 87.9k times · Source

What are the advantages of binary search trees over hash tables?

Hash tables can look up any element in Theta(1) time and it is just as easy to add an element....but I'm not sure of the advantages going the other way around.

Answer

Alex picture Alex · Nov 11, 2013

One advantage that no one else has pointed out is that binary search tree allows you to do range searches efficiently.

In order to illustrate my idea, I want to make an extreme case. Say you want to get all the elements whose keys are between 0 to 5000. And actually there is only one such element and 10000 other elements whose keys are not in the range. BST can do range searches quite efficiently since it does not search a subtree which is impossible to have the answer.

While, how can you do range searches in a hash table? You either need to iterate every bucket space, which is O(n), or you have to look for whether each of 1,2,3,4... up to 5000 exists. (what about the keys between 0 and 5000 are an infinite set? for example keys can be decimals)

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