Section 1Understand Problem
Section 01
Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
Problem statement
Given an input string `s` and a pattern `p`, implement regular expression matching with support for `'.'` and `'*'` where `'.'` matches any single character and `'*'` matches zero or more of the preceding element. The matching should cover the *entire* input string (not partial).
Example
s = "aa", p = "a" → false
Constraints
1 ≤ s.length ≤ 20 · 1 ≤ p.length ≤ 20 · s contains only lowercase letters · p contains lowercase letters, '.', and '*' · It is guaranteed that for each '*', there will be a previous valid character to match
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