Add Aho-Corasick in Python (jainaman224#2962)

Author: shivanidalmia1203

Aho-Corasick/Aho-Corasick.py

@@ -0,0 +1,89 @@
+# AhoNode class
+class AhoNode:
+    def __init__(self):
+        self.goto = {}
+        self.out = []
+        self.fail = None
+
+
+# creating aho forest
+def aho_create_forest(patterns):
+    root = AhoNode()
+
+    for path in patterns:
+        node = root
+        for symbol in path:
+            node = node.goto.setdefault(symbol, AhoNode())
+        node.out.append(path)
+    return root
+
+
+# Creating aho automata
+def aho_create_statemachine(patterns):
+    root = aho_create_forest(patterns)
+    queue = []
+    for node in root.goto.values():
+        queue.append(node)
+        node.fail = root
+
+    while len(queue) > 0:
+        rnode = queue.pop(0)
+
+        for key, unode in rnode.goto.items():
+            queue.append(unode)
+            fnode = rnode.fail
+            while fnode is not None and key not in fnode.goto:
+                fnode = fnode.fail
+            unode.fail = fnode.goto[key] if fnode else root
+            unode.out += unode.fail.out
+
+    return root
+
+
+def aho_find_all(s, root, callback):
+    node = root
+
+    for i in range(len(s)):
+        while node is not None and s[i] not in node.goto:
+            node = node.fail
+        if node is None:
+            node = root
+            continue
+        node = node.goto[s[i]]
+        for pattern in node.out:
+            callback(i - len(pattern) + 1, pattern)
+
+
+# Printing the position of pattern found
+def print_pattern(pos, patterns):
+    print("At pos %s found pattern: %s" % (pos, patterns))
+
+
+if __name__ == "__main__":
+    patterns = []
+
+    # taking inputs
+    n = int(input("Enter no. of elements :- "))
+    for i in range(0, n):
+        ele = input("Enter element :- ")
+        patterns.append(ele)
+    s = input("Enter text :- ")
+
+    root = aho_create_statemachine(patterns)
+    aho_find_all(s, root, print_pattern)
+
+ 
+"""
+INPUT:
+n=6
+patterns = ['a', 'ab', 'abc', 'bc', 'c', 'cba']
+s = "abcba"
+
+OUTPUT:
+At pos 0 found pattern: a
+At pos 0 found pattern: ab
+At pos 0 found pattern: abc
+At pos 1 found pattern: bc
+At pos 2 found pattern: c
+At pos 2 found pattern: cba
+"""