Regular Expression Matching

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Problem

Given a string s and a pattern p that may include '.' (matches any single character) and '*' (matches zero or more of the preceding element), implement regular expression matching that covers the entire input string.

Examples

Example 1

Input:s = "aa", p = "a"

Output:false

Example 2

Input:s = "aa", p = "a*"

Output:true

Constraints

1 <= s.length <= 20
1 <= p.length <= 30

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How to approach it: the 2-D Dynamic Programming pattern

The same DP idea as 1-D, but the state depends on two indices — often two positions in a grid, or a position in each of two sequences being compared.

Look for this pattern when

You're comparing two sequences (finding a longest common subsequence, edit distance).
You're computing paths or optimal values across a 2-D grid.

Read the full 2-D Dynamic Programming guide →

Video walkthroughs

Original problem on LeetCode ↗