Pyupgrade to Python 3.9 (#4718)

* Pyupgrade to Python 3.9

* updating DIRECTORY.md

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

strings/aho_corasick.py

@@ -1,5 +1,6 @@
+from __future__ import annotations
+
 from collections import deque
-from typing import Dict, List, Union
 
 
 class Automaton:
@@ -13,7 +14,7 @@ class Automaton:
             self.add_keyword(keyword)
         self.set_fail_transitions()
 
-    def find_next_state(self, current_state: int, char: str) -> Union[int, None]:
+    def find_next_state(self, current_state: int, char: str) -> int | None:
         for state in self.adlist[current_state]["next_states"]:
             if char == self.adlist[state]["value"]:
                 return state
@@ -63,7 +64,7 @@ class Automaton:
                     + self.adlist[self.adlist[child]["fail_state"]]["output"]
                 )
 
-    def search_in(self, string: str) -> Dict[str, List[int]]:
+    def search_in(self, string: str) -> dict[str, list[int]]:
         """
         >>> A = Automaton(["what", "hat", "ver", "er"])
         >>> A.search_in("whatever, err ... , wherever")

strings/boyer_moore_search.py

@@ -17,7 +17,7 @@ Time Complexity : O(n/m)
     n=length of main string
     m=length of pattern string
 """
-from typing import List
+from __future__ import annotations
 
 
 class BoyerMooreSearch:
@@ -59,7 +59,7 @@ class BoyerMooreSearch:
                 return currentPos + i
         return -1
 
-    def bad_character_heuristic(self) -> List[int]:
+    def bad_character_heuristic(self) -> list[int]:
         # searches pattern in text and returns index positions
         positions = []
         for i in range(self.textLen - self.patLen + 1):

strings/knuth_morris_pratt.py

@@ -1,4 +1,4 @@
-from typing import List
+from __future__ import annotations
 
 
 def kmp(pattern: str, text: str) -> bool:
@@ -36,7 +36,7 @@ def kmp(pattern: str, text: str) -> bool:
     return False
 
 
-def get_failure_array(pattern: str) -> List[int]:
+def get_failure_array(pattern: str) -> list[int]:
     """
     Calculates the new index we should go to if we fail a comparison
     :param pattern: