CareerCup

For hashtable,the date store and retrieve time is O(1).
while for BST,it is O(log2n).
But the BST is sorted while hash is not.
SO when you want to use sorted data and with little memory/time
to do it,you had better use BST

I think there are two trade-offs between a BST/map or a Hash Table

1) when the number of object to be inserted are relatively small
2) when need to iterate over the items inserted into your data-structure
for searching purpose
Then map/bst is preferred, since has relatively lower memory overhead
However with minor modification you can have iterators over hash table
also, but that incurs more memory overhead.

Comments welcome. :)

IMHO, the most important consideration is collision in hashtable.
The worst case for collision is the whole hashtable becomes a linked list, and it is O(n) to find a value.
The 2nd consideration is the insert/delete operation. It is less expensive to insert/delete for hashtalbe than BST. So if there are a lot of insertion/delete operations, hashtable is better.

Hash Table is recommended over Binary Search Tree
- When Data is in ascending/descending order
- Insertion/Deletion are not frequently required.
- Sorted sequence is not required.
- Searching is a prevalent operation.
- When data are comparatively less. When Data is more, Hashing might require more extra location to avoid Collision.

its when u know exact matches to match not just an approximation but indeed all the matches in a string.