Python/strings/wildcard_pattern_matching.py
P U N I T H 83cf5786cd
Add wildcard pattern matching using dynamic programming (#5334)
* Added regular expression implimentation using dp

* replaced input() with example values

* Apply suggestions from code review

Co-authored-by: Christian Clauss <cclauss@me.com>

* changed returning value to bool and added test cases

* added doctest

Co-authored-by: John Law <johnlaw.po@gmail.com>

* added test cases

* Apply suggestions from code review

Co-authored-by: John Law <johnlaw.po@gmail.com>

* shifted to strings

* Changed filename

* Update function name to match_pattern

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Update function name to match_pattern

Co-authored-by: John Law <johnlaw.po@gmail.com>

Co-authored-by: Christian Clauss <cclauss@me.com>
Co-authored-by: John Law <johnlaw.po@gmail.com>
2021-10-20 16:30:58 +08:00

113 lines
3.3 KiB
Python

"""
Implementation of 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).
"""
def match_pattern(input_string: str, pattern: str) -> bool:
"""
uses bottom-up dynamic programming solution for matching the input
string with a given pattern.
Runtime: O(len(input_string)*len(pattern))
Arguments
--------
input_string: str, any string which should be compared with the pattern
pattern: str, the string that represents a pattern and may contain
'.' for single character matches and '*' for zero or more of preceding character
matches
Note
----
the pattern cannot start with a '*',
because there should be at least one character before *
Returns
-------
A Boolean denoting whether the given string follows the pattern
Examples
-------
>>> match_pattern("aab", "c*a*b")
True
>>> match_pattern("dabc", "*abc")
False
>>> match_pattern("aaa", "aa")
False
>>> match_pattern("aaa", "a.a")
True
>>> match_pattern("aaab", "aa*")
False
>>> match_pattern("aaab", ".*")
True
>>> match_pattern("a", "bbbb")
False
>>> match_pattern("", "bbbb")
False
>>> match_pattern("a", "")
False
>>> match_pattern("", "")
True
"""
len_string = len(input_string) + 1
len_pattern = len(pattern) + 1
# dp is a 2d matrix where dp[i][j] denotes whether prefix string of
# length i of input_string matches with prefix string of length j of
# given pattern.
# "dp" stands for dynamic programming.
dp = [[0 for i in range(len_pattern)] for j in range(len_string)]
# since string of zero length match pattern of zero length
dp[0][0] = 1
# since pattern of zero length will never match with string of non-zero length
for i in range(1, len_string):
dp[i][0] = 0
# since string of zero length will match with pattern where there
# is at least one * alternatively
for j in range(1, len_pattern):
dp[0][j] = dp[0][j - 2] if pattern[j - 1] == "*" else 0
# now using bottom-up approach to find for all remaining lengths
for i in range(1, len_string):
for j in range(1, len_pattern):
if input_string[i - 1] == pattern[j - 1] or pattern[j - 1] == ".":
dp[i][j] = dp[i - 1][j - 1]
elif pattern[j - 1] == "*":
if dp[i][j - 2] == 1:
dp[i][j] = 1
elif pattern[j - 2] in (input_string[i - 1], "."):
dp[i][j] = dp[i - 1][j]
else:
dp[i][j] = 0
else:
dp[i][j] = 0
return bool(dp[-1][-1])
if __name__ == "__main__":
import doctest
doctest.testmod()
# inputing the strings
# input_string = input("input a string :")
# pattern = input("input a pattern :")
input_string = "aab"
pattern = "c*a*b"
# using function to check whether given string matches the given pattern
if match_pattern(input_string, pattern):
print(f"{input_string} matches the given pattern {pattern}")
else:
print(f"{input_string} does not match with the given pattern {pattern}")