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Regular Expression Matcher

Certification: Advanced Level Accuracy: 100% Submissions: 2 Points: 10

Write a Python function to implement a simple regular expression matcher with support for '.' and '*'.

Example 1
     
  • Input: text = "aa", pattern = "a*"
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  • Output: true
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  • Explanation: 
       
    • Step 1: '*' allows 'a' to repeat 0 or more times.
      •  
    • Step 2: Pattern "a*" matches "aa".
      •  
     
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Example 2
     
  • Input: text = "abc", pattern = "a.c"
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  • Output: true
    •  
  • Explanation: 
       
    • Step 1: '.' matches any character.
      •  
    • Step 2: Pattern "a.c" matches "abc" because '.' matches 'b'.
      •  
     
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Constraints
     
  • 1 ≤ text.length ≤ 20
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  • 1 ≤ pattern.length ≤ 30
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  • pattern contains only lowercase English letters, '.', and '*'
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  • Time Complexity: O(m * n), where m and n are the lengths of pattern and text
    •  
  • Space Complexity: O(m * n)
    •
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Hint
Solution

Solution Hints

    
  
  • Use dynamic programming to solve this problem
    • 
  
  • Create a 2D boolean array to store whether substrings of text match subpatterns
    • 
  
  • Handle the special cases of '*' and '.' carefully
    • 
  
  • Base case: empty pattern matches empty text
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  • Work through the pattern character by character, handling regular characters, dots, and stars differently
    •

Steps to solve by this approach:

 Step 1: Create a 2D DP table where dp[i][j] represents if the first i characters of text match the first j characters of pattern.
 Step 2: Set base case dp[0][0] = True (empty text matches empty pattern).
 Step 3: Handle the special case where pattern contains '*' that can match empty string.
 Step 4: Fill the table by checking character matches and applying the appropriate logic for '.', and '*'.
 Step 5: Return dp[len(text)][len(pattern)] which indicates if the entire text matches the entire pattern.

Submitted Code :