Balanced parentheses (#3768)

* Fixed balanced_parentheses.py

* fixed pre-commit

* eliminate is_paired

* remove unused line

* updating DIRECTORY.md

* Update data_structures/stacks/balanced_parentheses.py

Co-authored-by: Christian Clauss <cclauss@me.com>

* Add more test cases

* Update data_structures/stacks/balanced_parentheses.py

Co-authored-by: Christian Clauss <cclauss@me.com>

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

DIRECTORY.md

@@ -520,6 +520,7 @@
   * [Sierpinski Triangle](https://github.com/TheAlgorithms/Python/blob/master/other/sierpinski_triangle.py)
   * [Tower Of Hanoi](https://github.com/TheAlgorithms/Python/blob/master/other/tower_of_hanoi.py)
   * [Triplet Sum](https://github.com/TheAlgorithms/Python/blob/master/other/triplet_sum.py)
+  * [Two Pointer](https://github.com/TheAlgorithms/Python/blob/master/other/two_pointer.py)
   * [Two Sum](https://github.com/TheAlgorithms/Python/blob/master/other/two_sum.py)
   * [Word Patterns](https://github.com/TheAlgorithms/Python/blob/master/other/word_patterns.py)
 

data_structures/stacks/balanced_parentheses.py

@@ -1,23 +1,37 @@
 from .stack import Stack
 
-__author__ = "Omkar Pathak"
 
-
-def balanced_parentheses(parentheses):
-    """ Use a stack to check if a string of parentheses is balanced."""
-    stack = Stack(len(parentheses))
-    for parenthesis in parentheses:
-        if parenthesis == "(":
-            stack.push(parenthesis)
-        elif parenthesis == ")":
-            if stack.is_empty():
+def balanced_parentheses(parentheses: str) -> bool:
+    """Use a stack to check if a string of parentheses is balanced.
+    >>> balanced_parentheses("([]{})")
+    True
+    >>> balanced_parentheses("[()]{}{[()()]()}")
+    True
+    >>> balanced_parentheses("[(])")
+    False
+    >>> balanced_parentheses("1+2*3-4")
+    True
+    >>> balanced_parentheses("")
+    True
+    """
+    stack = Stack()
+    bracket_pairs = {"(": ")", "[": "]", "{": "}"}
+    for bracket in parentheses:
+        if bracket in bracket_pairs:
+            stack.push(bracket)
+        elif bracket in (")", "]", "}"):
+            if stack.is_empty() or bracket_pairs[stack.pop()] != bracket:
                 return False
-            stack.pop()
     return stack.is_empty()
 
 
 if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
+
     examples = ["((()))", "((())", "(()))"]
     print("Balanced parentheses demonstration:\n")
     for example in examples:
-        print(example + ": " + str(balanced_parentheses(example)))
+        not_str = "" if balanced_parentheses(example) else "not "
+        print(f"{example} is {not_str}balanced")