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Aho-Corasick Algorithm/aho_corasick1.py

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+# Python implementation of Aho-Corasick string matching
+FAIL = -1
+
+def aho_corasick(string, keywords):
+    transitions = {}
+    outputs = {}
+    fails = {}
+
+    new_state = 0
+
+    for keyword in keywords:
+        state = 0
+
+        for j, char in enumerate(keyword):
+            res = transitions.get((state, char), FAIL)
+            if res == FAIL:
+                break
+            state = res
+
+        for char in keyword[j:]:
+            new_state += 1
+            transitions[(state, char)] = new_state
+            state = new_state
+
+        outputs[state] = [keyword]
+
+    queue = []
+    for (from_state, char), to_state in transitions.items():
+        if from_state == 0 and to_state != 0:
+            queue.append(to_state)
+            fails[to_state] = 0
+
+    while queue:
+        r = queue.pop(0)
+        for (from_state, char), to_state in transitions.items():
+            if from_state == r:
+                queue.append(to_state)
+                state = fails[from_state]
+
+                while True:
+                    res = transitions.get((state, char), state and FAIL)
+                    if res != FAIL:
+                        break
+                    state = fails[state]
+
+                failure = transitions.get((state, char), state and FAIL)
+                fails[to_state] = failure
+                outputs.setdefault(to_state, []).extend(
+                    outputs.get(failure, []))
+
+    state = 0
+    results = []
+    for i, char in enumerate(string):
+        while True:
+            res = transitions.get((state, char), state and FAIL)
+            if res != FAIL:
+                state = res
+                break
+            state = fails[state]
+
+        for match in outputs.get(state, ()):
+            pos = i - len(match) + 1
+            results.append((pos, match))
+
+    return results