Implementation of the Knuth-Morris-Pratt (KMP) string matching algorithm

pydatastructs/strings/__init__.py

@@ -1,8 +1,18 @@
 __all__ = []
 
-from . import trie
+from . import (
+    trie,
+    string_matching_algorithms
+)
+
 from .trie import (
     Trie
 )
 
 __all__.extend(trie.__all__)
+
+from .string_matching_algorithms import (
+    find_string
+)
+
+__all__.extend(string_matching_algorithms.__all__)

pydatastructs/strings/string_matching_algorithms.py

@@ -0,0 +1,136 @@
+from pydatastructs.linear_data_structures.arrays import (
+    OneDimensionalArray)
+
+__all__ = [
+    'find_string'
+]
+
+def find_string(text: str, pattern: str, algorithm: str) -> bool:
+    """API of finding occurrence of a pattern string within another string or body of text.
+
+    Parameters
+    ----------
+    text: str
+        A text, set of characters can include alphabets, numbers , special characters and blank spaces
+    pattern: str
+        A text, set of characters can include alphabets, numbers , special characters and blank spaces
+    algorithm: str
+        A valid algorithm name
+
+    Returns
+    -------
+    bool
+        True if pattern occurs in the string, else False
+
+    Examples
+    --------
+    >>> from pydatastructs.strings.string_matching_algorithms import find_string
+    >>> find_string("aefoaefcdaefcdaed", "aefcdaed", algorithm = "kmp")
+    True
+    >>> find_string("aefoaefcdaefcdaed", "aefcdaedz", algorithm = "kmp")
+    False
+
+    """
+    return eval(algorithm + "('" + text + "','" + pattern + "')")
+
+
+def kmp(string: str, substring: str) -> bool:
+    """Determine whether the substring appears somewhere in the string using Knuth–Morris–Pratt algorithm
+
+    Parameters
+    ----------
+    string: str
+        A text, set of characters
+    substring: str
+        A pattern/substring that is searched for in the string
+
+    Returns
+    -------
+    bool
+        Whether substring exists in the string or not
+
+    Examples
+    --------
+    >>> from pydatastructs.strings.string_matching_algorithms import kmp
+    >>> kmp("aefoaefcdaefcdaed", "aefcdaed")
+    True
+    >>> kmp("aefoaefcdaefcdaed", "aefcdaedz")
+    False
+
+    References
+    -------
+    .. [1] https://www.inf.hs-flensburg.de/lang/algorithmen/pattern/kmpen.htm
+    .. [2] https://towardsdatascience.com/pattern-search-with-the-knuth-morris-pratt-kmp-algorithm-8562407dba5b
+    .. [3] https://iopscience.iop.org/article/10.1088/1742-6596/1345/4/042005/pdf
+
+    """
+    patternsInSubString = _buildPattern(substring)
+    return _doMatch(string, substring, patternsInSubString)
+
+
+def _buildPattern(substring: str) -> OneDimensionalArray:
+    """Check for patterns existing in the substring
+
+    Parameters
+    ----------
+    substring: str
+        A text, set of characters
+
+    Returns
+    -------
+    patterns: OneDimensionalArray
+        Returns an array of indicies. For a given index if value > -1
+        represents that the suffix found at the index, is also the prefix
+        at the value index. If value is -1, then there is no prefix that is also
+        a suffix.
+
+    """
+    j = 0
+    i = 1
+    patterns = OneDimensionalArray(int, len(substring))
+    patterns.fill(-1)
+    while i < len(substring):
+        if substring[i] is substring[j]:
+            # A prefix that is also a suffix
+            patterns[i] = j
+            i += 1
+            j += 1
+        elif j > 0:
+            # Check the previous existing pattern
+            j = patterns[j - 1] + 1
+        else:
+            i += 1
+    return patterns
+
+
+def _doMatch(string: str, substring: str, patterns: OneDimensionalArray) -> bool:
+    """Check if the string exists in the substring
+
+    Parameters
+    ----------
+    string: str
+        A text, set of characters
+    substring: str
+        A pattern/substring that is searched for in the string
+    patterns: OneDimensionalArray
+        An array of integers, each value < len(patterns)
+
+    Returns
+    -------
+    bool
+        Whether substring exists in the string or not
+
+    """
+    i = 0
+    j = 0
+    while i < len(string):
+        if string[i] is substring[j]:
+            i += 1
+            j += 1
+        elif j > 0:
+            j = patterns[j - 1] + 1
+        else:
+            i += 1
+        if j is len(substring):
+            return True
+    return False

pydatastructs/strings/tests/test_string_matching_algorithms.py

@@ -0,0 +1,26 @@
+from pydatastructs.strings.string_matching_algorithms import find_string
+
+def test_kms():
+    _test_common_string_matching('kmp')
+
+
+def _test_common_string_matching(algorithm):
+    true_text_pattern_dictionary = {
+        "Knuth-Morris-Pratt": "-Morris-",
+        "abcabcabcabdabcabdabcabca": "abcabdabcabca",
+        "aefcdfaecdaefaefcdaefeaefcdcdeae": "aefcdaefeaefcd",
+        "aaaaaaaa": "aaa",
+        "fullstringmatch": "fullstringmatch"
+    }
+    for test_case_key in true_text_pattern_dictionary:
+        assert find_string(test_case_key, true_text_pattern_dictionary[test_case_key], algorithm) is True
+
+    false_text_pattern_dictionary = {
+        "Knuth-Morris-Pratt": "-Pratt-",
+        "abcabcabcabdabcabdabcabca": "qwertyuiopzxcvbnm",
+        "aefcdfaecdaefaefcdaefeaefcdcdeae": "cdaefaefe",
+        "fullstringmatch": "fullstrinmatch"
+    }
+
+    for test_case_key in false_text_pattern_dictionary:
+        assert find_string(test_case_key, false_text_pattern_dictionary[test_case_key], algorithm) is False