Created
January 24, 2019 20:51
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#!/usr/bin/env python3 | |
""" | |
Write a function that takes two strings as arguments, s and p, | |
and returns a boolean denoting whether s matches p. | |
p is a sequence of any number of the following: | |
1. a-z - which stands for itself | |
2. . - which matches any character | |
3. * - which matches 0 or more occurences of the previous single character | |
s = "aba", p = "ab" -> false | |
s = "aa", p = "a*" -> true | |
s = "ab", p = ".*" -> true | |
s = "ab", p = "." -> false | |
s = "aab", p = "c*a*b" -> true | |
s = "aaa", p = "a*." -> true | |
""" | |
def is_match(s: str, p: str) -> bool: | |
"""Checks whether s matches p. | |
Here, p is a sequence of any number of the following: | |
1. a-z - which stands for itself | |
2. . - which matches any character | |
3. * - which matches 0 or more occurences of the previous single character | |
Args: | |
s: any string | |
p: a regex-like pattern | |
Returns: | |
A boolean denoting whether s matches p. | |
""" | |
# pattern and string both empty: match | |
if len(s) == 0 and len(p) == 0: | |
return True | |
# pattern empty but not string: no match | |
if len(p) == 0: | |
return False | |
# 0+ occurences: | |
if len(p) >= 2 and p[1] == '*': | |
# string empty but not pattern | |
if len(s) == 0: | |
return is_match(s, p[2:]) | |
# is_match(s, p[2:]): 0 occurences | |
# is_match(s[1:], p): 1+ occurence | |
return is_match(s, p[2:]) or is_match(s[1:], p) | |
# string empty but not pattern: no match | |
# (all following checks require 1+ characters in string) | |
if len(s) == 0: | |
return False | |
# any character | |
if p[0] == '.': | |
return is_match(s[1:], p[1:]) | |
# specific character | |
if s[0] == p[0]: | |
return is_match(s[1:], p[1:]) | |
return False | |
def _test_is_match() -> None: | |
assert(is_match('aba', 'ab') == False) | |
assert(is_match('aa', 'a*') == True) | |
assert(is_match('ab', '.*') == True) | |
assert(is_match('ab', '.') == False) | |
assert(is_match('aab', 'c*a*b') == True) | |
assert(is_match('aaa', 'a*a') == True) | |
def main(): | |
_test_is_match() | |
print('The is_match function passed all tests.') | |
if __name__ == '__main__': | |
main() |
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