mirror of
https://github.com/TheAlgorithms/Python.git
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83cf5786cd
* 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>
113 lines
3.3 KiB
Python
113 lines
3.3 KiB
Python
"""
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Implementation of regular expression matching with support for '.' and '*'.
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'.' Matches any single character.
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'*' Matches zero or more of the preceding element.
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The matching should cover the entire input string (not partial).
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"""
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def match_pattern(input_string: str, pattern: str) -> bool:
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"""
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uses bottom-up dynamic programming solution for matching the input
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string with a given pattern.
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Runtime: O(len(input_string)*len(pattern))
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Arguments
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--------
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input_string: str, any string which should be compared with the pattern
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pattern: str, the string that represents a pattern and may contain
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'.' for single character matches and '*' for zero or more of preceding character
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matches
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Note
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----
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the pattern cannot start with a '*',
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because there should be at least one character before *
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Returns
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-------
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A Boolean denoting whether the given string follows the pattern
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Examples
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-------
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>>> match_pattern("aab", "c*a*b")
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True
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>>> match_pattern("dabc", "*abc")
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False
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>>> match_pattern("aaa", "aa")
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False
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>>> match_pattern("aaa", "a.a")
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True
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>>> match_pattern("aaab", "aa*")
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False
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>>> match_pattern("aaab", ".*")
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True
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>>> match_pattern("a", "bbbb")
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False
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>>> match_pattern("", "bbbb")
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False
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>>> match_pattern("a", "")
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False
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>>> match_pattern("", "")
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True
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"""
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len_string = len(input_string) + 1
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len_pattern = len(pattern) + 1
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# dp is a 2d matrix where dp[i][j] denotes whether prefix string of
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# length i of input_string matches with prefix string of length j of
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# given pattern.
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# "dp" stands for dynamic programming.
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dp = [[0 for i in range(len_pattern)] for j in range(len_string)]
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# since string of zero length match pattern of zero length
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dp[0][0] = 1
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# since pattern of zero length will never match with string of non-zero length
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for i in range(1, len_string):
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dp[i][0] = 0
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# since string of zero length will match with pattern where there
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# is at least one * alternatively
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for j in range(1, len_pattern):
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dp[0][j] = dp[0][j - 2] if pattern[j - 1] == "*" else 0
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# now using bottom-up approach to find for all remaining lengths
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for i in range(1, len_string):
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for j in range(1, len_pattern):
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if input_string[i - 1] == pattern[j - 1] or pattern[j - 1] == ".":
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dp[i][j] = dp[i - 1][j - 1]
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elif pattern[j - 1] == "*":
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if dp[i][j - 2] == 1:
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dp[i][j] = 1
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elif pattern[j - 2] in (input_string[i - 1], "."):
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dp[i][j] = dp[i - 1][j]
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else:
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dp[i][j] = 0
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else:
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dp[i][j] = 0
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return bool(dp[-1][-1])
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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# inputing the strings
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# input_string = input("input a string :")
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# pattern = input("input a pattern :")
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input_string = "aab"
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pattern = "c*a*b"
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# using function to check whether given string matches the given pattern
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if match_pattern(input_string, pattern):
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print(f"{input_string} matches the given pattern {pattern}")
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else:
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print(f"{input_string} does not match with the given pattern {pattern}")
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