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Morris-Pratt

Morris-Pratt uses using prefix borders to avoid rechecking matched characters for exact string matching.

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Quick Facts

Compact metadata for implementation and discovery.

Category: Pattern Matching
Difficulty: Intermediate
Family: String Matching
Tier: Core
Status: Verified
Review: Source Checked
Sources: 2
Formulas: 0
Relationships: 3
Code example: Ready
Visualization: Ready

Overview

Morris-Pratt handles exact string matching by using prefix borders to avoid rechecking matched characters.

Core Concepts

exact string matchingstring matchingmatchingpattern matching

Quick facts

Complexity

Runtime and memory behavior at a glance.

Best

O(n)

Average

O(n + m)

Worst

O(n + m)

Space

O(n + m)

When to Use

Use Morris-Pratt when solving string matching and you want to benefit from using prefix borders to avoid rechecking matched characters.
Choose it when O(n + m) average/worst-case time and O(n + m) memory match your workload profile.
Prefer it over Bit-Parallel Levenshtein or Shift-And Algorithm when the problem structure favors exact string matching.

When Not to Use

Avoid when preprocessing cost is larger than the savings for a one-off tiny input.
Avoid when the alphabet or scoring assumptions do not match the sequence data.

What It Does

Morris-Pratt uses using prefix borders to avoid rechecking matched characters for exact string matching
Organizes the work around exact string matching and string matching.

Use Cases

Production and research workloads requiring string matching via using prefix borders to avoid rechecking matched characters.
String Matching pipelines where O(n + m) time and O(n + m) space fit system constraints.
Engineering comparisons against Bit-Parallel Levenshtein and Shift-And Algorithm when tuning string matching.

Inputs

Text or sequence
Pattern, index, or comparison sequence

Outputs

Matches, alignment, index, or similarity value

Pseudocode

1.Preprocess the input alphabet, pattern/grammar rules, or symbol frequency tables for Morris-Pratt.
2.Construct the lookup automaton, suffix/shift index, or coding state (exact string matching, string matching).
3.Scan the input sequence by using prefix borders to avoid rechecking matched characters.
4.Emit matches, derivation nodes, or encoded tokens while advancing the state transition table.
5.Finalize trailing state and return the completed string matching output.

Canonical Example

Input: Text or sequence configured for a representative string matching test case
Output: Matches, alignment, index, or similarity value satisfying Morris-Pratt invariants
Explanation: Morris-Pratt processes the input by using prefix borders to avoid rechecking matched characters, tracking exact string matching and string matching to produce the verified string matching result.

Implementation Notes

Keep preprocessing output inspectable with short examples.
Test repeated characters and overlapping matches.
Document sentinel or alphabet assumptions.

Common Pitfalls

Mishandling empty patterns, repeated characters, or sentinel symbols.
Confusing preprocessing indexes with the query algorithm.
Forgetting whether indexing is zero-based or one-based.

Interactive Mechanism Walkthrough

Sequence Window & Automaton Alignment

Show using prefix borders to avoid rechecking matched characters on a small exact string matching example.

Input:ABABABCABAB

Window:ABAB

Step 1 of 5: Preprocess the input alphabet, pattern/grammar rules, or symbol frequency tables for Morris-Pratt.

pattern-matching-mechanism

Notes

Morris-Pratt operates in O(n + m) time and O(n + m) space within the String Matching family. Often compared with Bit-Parallel Levenshtein and Shift-And Algorithm.