example1

# example1 - Describing Regular Expressions CMSC 330...

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1 CMSC 330: Organization of Programming Languages Examples of REs & Finite Automata CMSC 330 2 Describing Regular Expressions a) 0(0|1)*0 All strings beginning and ending in 0 b) (( |0)1*)* All strings c) (0|1)*0(0|1)(0|1) All strings with 0 as third digit from right CMSC 330 3 Creating Regular Expressions For all strings of 0’s and 1’s that… a) Begin in 1 1(0|1)* b) End in 1 (0|1)*1 c) Contains 00 (0|1)*00(0|1)* d) Do not contain 00 (01|1)*( |0) CMSC 330 4 Creating NFA For all strings of 0’s and 1’s that… a) Begin in 1 b) End in 1 c) Contains 00 d) Do not contain 00 1 0,1 1 0 0 0,1 0 0,1 0,1 1 0 Based on regular expression CMSC 330 5 Creating DFA For all strings of 0’s and 1’s that… a) Begin in 1 b) End in 1 c) Contains 00 d) Do not contain 00 1 0 0,1 0 1 1 0 0 1 1 0,1 0 0 1 1 0,1 Swap final / non-final states! CMSC 330 6 a) Construct NFA b) Accept ababbab 7,5,1,2,6,8,7,5,3,4,6,8,7,5,1,2,6,8,7,5,3,4,6,8,7,5,3,4,6, 8,7,5,1,2,6,8,7,5,3,4,6,8 accept For RE (a | b )* a 3 4 b 1 2 5 6 7 8

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2 CMSC 330 7 For RE (a | b )* c) Reduce NFA to DFA Start = ε -closure(7) = {7,5,1,3,8} R = {{7,5,1,3,8}} r R = {7,5,1,3,8 } // mark DFA state move ({7,5,1,3,8}, a) = {2} e = ε -closure({2}) = {2,6,8,7,5,1,3}
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