API improvements

Author: czgdp1807

pydatastructs/strings/__init__.py

@@ -2,7 +2,7 @@
 
 from . import (
     trie,
-    string_matching_algorithms
+    algorithms
 )
 
 from .trie import (
@@ -11,8 +11,8 @@
 
 __all__.extend(trie.__all__)
 
-from .string_matching_algorithms import (
-    find_string
+from .algorithms import (
+    find
 )
 
-__all__.extend(string_matching_algorithms.__all__)
+__all__.extend(algorithms.__all__)

pydatastructs/strings/algorithms.py

@@ -0,0 +1,109 @@
+from pydatastructs.linear_data_structures.arrays import (
+    DynamicOneDimensionalArray, OneDimensionalArray)
+
+__all__ = [
+    'find'
+]
+
+def find(text, query, algorithm):
+    """
+    Finds occurrence of a query string within the text string.
+
+    Parameters
+    ==========
+
+    text: str
+        The string on which query is to be performed.
+    query: str
+        The string which is to be searched in the text.
+    algorithm: str
+        The algorithm which should be used for
+        searching.
+        Currently the following algorithms are
+        supported,
+        'kmp' -> Knuth-Morris-Pratt as given in [1].
+
+    Returns
+    =======
+
+    DynamicOneDimensionalArray
+        An array of starting positions of the portions
+        in the text which match with the given query.
+
+    Examples
+    ========
+
+    >>> from pydatastructs.strings.algorithms import find
+    >>> text = "abcdefabcabe"
+    >>> pos = find(text, "ab", algorithm="kmp")
+    >>> str(pos)
+    "['0', '6', '9']"
+    >>> pos = find(text, "abc", algorithm="kmp")
+    >>> str(pos)
+    "['0', '6']"
+    >>> pos = find(text, "abe", algorithm="kmp")
+    >>> str(pos)
+    "['9']"
+    >>> pos = find(text, "abed", algorithm="kmp")
+    >>> str(pos)
+    '[]'
+
+    References
+    ==========
+
+    .. [1] https://www.inf.hs-flensburg.de/lang/algorithmen/pattern/kmpen.htm
+    """
+    import pydatastructs.strings.algorithms as algorithms 
+    func = "_" + algorithm
+    if not hasattr(algorithms, func): 
+        raise NotImplementedError( 
+        "Currently %s algoithm for searching strings "
+        "inside a text isn't implemented yet."
+        %(algorithm)) 
+    return getattr(algorithms, func)(text, query)
+
+
+def _knuth_morris_pratt(text, query):
+    kmp_table = _build_kmp_table(query)
+    return _do_match(text, query, kmp_table)
+
+_kmp = _knuth_morris_pratt
+
+def _build_kmp_table(query):
+    pos, cnd = 1, 0
+    kmp_table = OneDimensionalArray(int, len(query) + 1)
+
+    kmp_table[0] = -1
+
+    while pos < len(query):
+        if query[pos] == query[cnd]:
+            kmp_table[pos] = kmp_table[cnd]
+        else:
+            kmp_table[pos] = cnd
+            while cnd >= 0 and query[pos] != query[cnd]:
+                cnd = kmp_table[cnd]
+        pos, cnd = pos + 1, cnd + 1
+    kmp_table[pos] = cnd
+
+    return kmp_table
+
+
+
+def _do_match(string, query, kmp_table):
+    j, k = 0, 0
+    positions = DynamicOneDimensionalArray(int, 0)
+
+    while j < len(string):
+        if query[k] == string[j]:
+            j = j + 1
+            k = k + 1
+            if k == len(query):
+                positions.append(j - k)
+                k = kmp_table[k]
+        else:
+            k = kmp_table[k]
+            if k < 0:
+                j = j + 1
+                k = k + 1
+
+    return positions