Use Thompson's algorithm to build the NFA for the following regular expression. Build the corresponding DFA and minimize it.
- ((ε|a)b)*
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The non-deterministic finite automaton (NFA), built by applying Thompson's algorithm to the regular expression '''<nowiki>((ε|a)b)*</nowiki>''' is the following: | The non-deterministic finite automaton (NFA), built by applying Thompson's algorithm to the regular expression '''<nowiki>((ε|a)b)*</nowiki>''' is the following: | ||
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digraph nfa { | digraph nfa { | ||
{ node [shape=circle style=invis] start } | { node [shape=circle style=invis] start } | ||
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7 -> 1; 7 -> 8 | 7 -> 1; 7 -> 8 | ||
fontsize=10 | fontsize=10 | ||
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} | } | ||
| − | </ | + | </dot-hack> |
Applying the determination algorithm to the above NFA, the following determination table is obtained: | Applying the determination algorithm to the above NFA, the following determination table is obtained: | ||
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! style="text-align: left; font-weight:normal; vertical-align: top; width: 50%;" |Graphically, the DFA is represented as follows: | ! style="text-align: left; font-weight:normal; vertical-align: top; width: 50%;" |Graphically, the DFA is represented as follows: | ||
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digraph dfa { | digraph dfa { | ||
{ node [shape=circle style=invis] start } | { node [shape=circle style=invis] start } | ||
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2 -> 2 [label="b"] | 2 -> 2 [label="b"] | ||
fontsize=10 | fontsize=10 | ||
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} | } | ||
| − | </ | + | </dot-hack> |
Given the minimization tree to the right, the final minimal DFA is: | Given the minimization tree to the right, the final minimal DFA is: | ||
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digraph dfamin { | digraph dfamin { | ||
{ node [shape=circle style=invis] start } | { node [shape=circle style=invis] start } | ||
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1 -> 02 [label="b"] | 1 -> 02 [label="b"] | ||
fontsize=10 | fontsize=10 | ||
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} | } | ||
| − | </ | + | </dot-hack> |
! style="text-align: left; font-weight:normal; vertical-align: top; width: 50%;" | The minimization tree is as follows. | ! style="text-align: left; font-weight:normal; vertical-align: top; width: 50%;" | The minimization tree is as follows. | ||
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digraph mintree { | digraph mintree { | ||
node [shape=none,fixedsize=true,width=0.2,fontsize=10] | node [shape=none,fixedsize=true,width=0.2,fontsize=10] | ||
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"{0, 2}" -> "{0,2} " [label=" a,b",fontsize=10] | "{0, 2}" -> "{0,2} " [label=" a,b",fontsize=10] | ||
fontsize=10 | fontsize=10 | ||
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} | } | ||
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|} | |} | ||
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</div> | </div> | ||
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[[en:Theoretical Aspects of Lexical Analysis]] | [[en:Theoretical Aspects of Lexical Analysis]] | ||
Problem
Use Thompson's algorithm to build the NFA for the following regular expression. Build the corresponding DFA and minimize it.
Solution
The non-deterministic finite automaton (NFA), built by applying Thompson's algorithm to the regular expression ((ε|a)b)* is the following:
Applying the determination algorithm to the above NFA, the following determination table is obtained:
| In | α∈Σ | move(In, α) | ε-closure(move(In, α)) | In+1 = ε-closure(move(In, α)) |
|---|---|---|---|---|
| - | - | 0 | 0, 1, 2, 3, 4, 6, 8 | 0 |
| 0 | a | 5 | 5, 6 | 1 |
| 0 | b | 7 | 1, 2, 3, 4, 6, 7, 8 | 2 |
| 1 | a | - | - | - |
| 1 | b | 7 | 1, 2, 3, 4, 6, 7, 8 | 2 |
| 2 | a | 5 | 5, 6 | 1 |
| 2 | b | 7 | 1, 2, 3, 4, 6, 7, 8 | 2 |
| Graphically, the DFA is represented as follows:
Given the minimization tree to the right, the final minimal DFA is: |
The minimization tree is as follows. |
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