Regular Expressions I
Computer Science
Level
3
Let R be the language described by the following regular expression:
(a|b)*(c|d)e?f+
How many of the following strings are NOT members of R ?
abc, aabbd, df, abbcdf, abdef, bbacf,
abbbbbbdef, aabbcef, abbceef, abababcf,
abcdf, f, ef, def, be, abe, acef
The answer is 9.
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1 solution
(a|b)*(c|d)e?f+ describes a language where the strings follow the following pattern: (0 or more a's and b's) followed by (1 c or 1d) followed by (0 e's or 1 e) followed by (1 or more f's).
The 9 strings in bold are not members of R :
abc , aabbd , df, abbcdf , abdef, bbacf, abbbbbbdef, aabbcef, abbceef , abababcf, abcdf , f , ef , def, be , abe , acef