Implement regular expression matching with support for '.' and '*'. '.' Matches any single character. '*' Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). The function prototype should be: bool is_match(const char *s, const char *p) Some examples: is_match("aa","a") → false is_match("aa","aa") → true is_match("aaa","aa") → false is_match("aa", "a*") → true is_match("aa", ".*") → true is_match("ab", ".*") → true is_match("aab", "c*a*b") → true """ def is_match(str_a, str_b):     """Finds if `str_a` matches `str_b`     Keyword arguments:     str_a -- string     str_b -- string     """     len_a, len_b = len(str_a) + 1, len(str_b) + 1     matches = [[False] * len_b  for _ in range(len_a)]     # Match empty string with empty pattern     matches[0][0] = True     # Match empty string with .*     for i, element in enumerate(str_b[1:], 2):         matches[0][i] = matches[0][i - 2] and element == '*'     for i, char_a in enumerate(str_a, 1):         for j, char_b in enumerate(str_b, 1):             if char_b != '*':                 # The previous character has matched and the current one                 # has to be matched. Two possible matches: the same or .                 matches[i][j] = matches[i - 1][j - 1] and \                                 char_b in (char_a, '.')             else:                 # Horizontal look up [j - 2].                 # Not use the character before *..  Complete.

Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
Problem 1PE
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Q8. 

Implement regular expression matching with support for '.' and '*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

The function prototype should be:
bool is_match(const char *s, const char *p)

Some examples:
is_match("aa","a") → false
is_match("aa","aa") → true
is_match("aaa","aa") → false
is_match("aa", "a*") → true
is_match("aa", ".*") → true
is_match("ab", ".*") → true
is_match("aab", "c*a*b") → true
"""

def is_match(str_a, str_b):
    """Finds if `str_a` matches `str_b`

    Keyword arguments:
    str_a -- string
    str_b -- string
    """
    len_a, len_b = len(str_a) + 1, len(str_b) + 1
    matches = [[False] * len_b  for _ in range(len_a)]

    # Match empty string with empty pattern
    matches[0][0] = True

    # Match empty string with .*
    for i, element in enumerate(str_b[1:], 2):
        matches[0][i] = matches[0][i - 2] and element == '*'

    for i, char_a in enumerate(str_a, 1):
        for j, char_b in enumerate(str_b, 1):
            if char_b != '*':
                # The previous character has matched and the current one
                # has to be matched. Two possible matches: the same or .
                matches[i][j] = matches[i - 1][j - 1] and \
                                char_b in (char_a, '.')
            else:
                # Horizontal look up [j - 2].
                # Not use the character before *.. 

Complete. 

 

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