Regular Expression Matching
Check if string s matches pattern p '.' matches any single character '*' matches zero or more of the preceding element Example: s = "aa", p = "a" => false (doesn't cover entire string) Example: s = "aa", p = "a*" => true ('*' means zero or more 'a') Example: s = "ab", p = ".*" => true ('.*' matches any string)
Regular Expression Matching is about turning repeated work into a reusable state instead of re-solving subproblems. It's a hard one for a reason: it stresses state-and-transition thinking when the rules pile up. Don't rush the code—spend your time nailing the state definition first.
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