Computer Science 226
Algorithms and Data Structures
Spring 2013
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Course Information |
Assignments |
Exercises |
Lectures |
Exams |
Precepts |
Booksite
Regular Expressions
Things to Know Before Lecture
- The syntax of regular expressions.
- How to manually tell if a string matches a regular expression.
- How to write a regular expression to meet a simple spec.
- Optional but recommended:
- What an NFA is.
- How to read an NFA diagram (red arrows and black arrows).
- How to simulate an NFA manually to test if a string matches a regular expression.
Pre-Lecture Preparation Guide.
High priority topics are in red. Medium priority topics are in green. Low priority topics are in blue.
Checkpoint 1:
How many bitstrings of length exactly 1,000 match the regular expression 0(0 | 1)*1?
Answer (highlight to see): 2998 - in English, the regular expression matches for any bit string that starts with 0 and ends with 1. That leaves 998 unspecified characters in the middle which may be either 0 or 1.
Checkpoint 2 (optional but recommended): Given the NFA below, which of the following strings match? What is the set of possible states that the DFA could reach with this input?
- AB - No, NFA is in state 5, 8, or 9. This set does not include the accept state (#11).
- ABD - Yes, NFA is in state 10 or 11. This set includes the accept state.
- BD - No. There are no valid states.
- AC - No. NFA is in state 8 or 9.
- ACD - Yes, NFA is in state 10 or 11.
- AACD - No. There are no valid states.
