Overview
Bitap packs pattern-prefix state into machine words, making exact or approximate matching fast for short patterns.
ExtendedSource checked
Bitap Algorithm
Searches for patterns by updating bit masks that represent matching prefixes.
Quick Facts
Compact metadata for implementation and discovery.
- Category
- Pattern Matching
- Difficulty
- Advanced
- Family
- Bit-Parallel String Search
- Tier
- Extended
- Status
- Verified
- Review
- Source Checked
- Sources
- 2
- Formulas
- 1
- Relationships
- 2
- Code example
- Ready
- Visualization
- Ready
Core Concepts
bit maskpattern prefixstate updateword parallelism
Quick facts
Complexity
Runtime and memory behavior at a glance.
Best
O(n)
Average
O(n)
Worst
O(n)
Space
O(pattern length / word size)
When to Use
- Use when text search needs bit mask.
- Use when the input matches the assumptions behind bit-Parallel String Search.
When Not to Use
- Avoid when a simpler exact search is enough and approximate scoring is unnecessary.
- Avoid when a simpler algorithm gives the required result with less setup.
What It Does
- Searches for patterns by updating bit masks that represent matching prefixes
- Uses bit mask and pattern prefix to guide the work.
- Produces matches.
Use Cases
- Text search
- Sequence comparison
- Similarity detection
Inputs
- Pattern or query sequence
- Text or target sequence
Outputs
- Matches
- Score
- Alignment or index
Key Formulas (1)
Bitap update
state = ((state << 1) | 1) & mask[char]
state = ((state << 1) | 1) & mask[char]Updates bit masks that track active pattern prefixes.
Pseudocode
- 1.Prepare the inputs and state needed for Bitap Algorithm.
- 2.Apply the bit mask step while the stopping condition has not been met.
- 3.Update intermediate state and discard invalid candidates.
- 4.Return matches.
Canonical Example
- Input
- Bitap Algorithm input with a small representative case
- Output
- Matches
- Explanation
- Bitap Algorithm applies bit mask to produce matches.
Implementation Notes
- Normalize input consistently before building indexes or comparing sequences.
- Keep the bit mask step separate enough to test independently.
Common Pitfalls
- Changing tokenization or distance definitions changes the match result.
- Forgetting to check edge cases can make Bitap Algorithm look correct on only ideal inputs.
Interactive Mechanism Walkthrough
Sequence Window & Automaton AlignmentShow matched positions, dynamic-programming cells, or candidate buckets.
Input:ABABABCABAB
Window:ABAB
Step 1 of 4: Prepare the inputs and state needed for Bitap Algorithm.
pattern-matching-mechanismNotes
Bitap Algorithm should be used with the assumptions and tradeoffs of bit-Parallel String Search in mind.
Sources (2)
What each reference supports for this entry.
Flexible Pattern Matching in Strings
BookPattern-matching reference covering Bitap Algorithm approximate matching model, string similarity measure, or bit-parallel search strategy.
Baeza-Yates-Gonnet Shift-Or
PaperSpecific reference for bit-parallel shift-or text searching and bitmask-based pattern matching.
Open sourceExplore Next
Good next jumps from the relationship graph, ranked for useful discovery.
Relationships
View full relationship pageAlternative toKnuth-Morris-Pratt
Bitap uses bit-parallel state updates rather than prefix-function transitions.
Conceptual neighborRegular Expression Matching
Bitap can support approximate or regular-expression-like matching variants.
Related Algorithms
Tags
Pattern MatchingStringsBit LevelSearch