- Problem description"
- Given a text document:
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx....
(Each x represents a character)
- Index the document so we can search for any pattern in the document.
- Given a text document:
- Prelude to a solution:
- A pattern can
found
starting in these places:
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.... ||||||| ... ||||||+---------> |||||+----------> ||||+-----------> |||+------------> ||+-------------> |+--------------> +--------------->
- A pattern can
found
starting in these places:
- Suffix trie:
- The suffix trie stores the set of strings that are all the possible suffixes of an input text
- Example:
- Input text: minimize
- All
possible suffixes:
- minimize
- inimize
- nimize
- imize
- mize
- ize
- ze
- e
- This is the same set
of patterns
that can be
found in the input
minimize:
minimize |||||||+ ===> e ||||||+- ===> ze |||||+-> ===> ize ||||+--> ===> mize |||+---> ===> imize ||+----> ===> nimize |+-----> ===> inimize +------> ===> minimize
- Input text: minimize
- Storing all suffixes of
minimize in
a (ordinary) trie:
- Sort the
suffixes (will help)
e e ze imize ize inimize mize ===> ize imize minimize nimize mize inimize nimize minimize ze
- Trie:
- Sort the
suffixes (will help)
- The Compressed suffix trie:
This is also the:
- Suffix tree of the text minimize
- The suffix trie is used
as a preprocessed index
for fast keyword retrieval
in an electronic document
- Example:
indexing all patterns
found in the
document containing the
text "minimize"
- Note:
- The leaf nodes store positions where the pattern starts in the document
- How to
search for
a pattern
using the
suufix tree:
- Example:
- Search for the pattern "im" in the document
- Traverse the suffix trie
using the search pattern "im":
- Example: