feat(algorithms stacks): reverse string character array

DIRECTORY.md

@@ -369,10 +369,24 @@
     * Shell Sort
       * [Test Shell Sort](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/sorting/shell_sort/test_shell_sort.py)
   * Stack
+    * Asteroid Collision
+      * [Test Asteroid Collision](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/asteroid_collision/test_asteroid_collision.py)
+    * Bracket Validator
+      * [Test Bracket Validator](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/bracket_validator/test_bracket_validator.py)
     * Daily Temperatures
       * [Test Daily Temperatures](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/daily_temperatures/test_daily_temperatures.py)
+    * Decimal To Binary
+      * [Test Decimal To Binary](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/decimal_to_binary/test_decimal_to_binary.py)
+    * Decode String
+      * [Test Decode String](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/decode_string/test_decode_string.py)
     * Minimum String Length After Removing Substrings
       * [Test Min Str Length After Removing Substrings](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/minimum_string_length_after_removing_substrings/test_min_str_length_after_removing_substrings.py)
+    * Nextgreater
+      * [Test Next Greater](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/nextgreater/test_next_greater.py)
+    * Removing Stars
+      * [Test Remove Starts](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/removing_stars/test_remove_starts.py)
+    * Reverse String
+      * [Test Reverse String](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/stack/reverse_string/test_reverse_string.py)
   * Strings
     * Caeser Cipher
       * [Test Caeser](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/strings/caeser_cipher/test_caeser.py)
@@ -901,21 +915,6 @@
   * Queue
     * Recent Counter
       * [Test Recent Calls](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/queue/recent_counter/test_recent_calls.py)
-  * Stack
-    * Asteroid Collision
-      * [Test Asteroid Collision](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/asteroid_collision/test_asteroid_collision.py)
-    * Bracket Validator
-      * [Test Bracket Validator](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/bracket_validator/test_bracket_validator.py)
-    * Decimal To Binary
-      * [Test Decimal To Binary](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/decimal_to_binary/test_decimal_to_binary.py)
-    * Decode String
-      * [Test Decode String](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/decode_string/test_decode_string.py)
-    * Nextgreater
-      * [Test Next Greater](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/nextgreater/test_next_greater.py)
-    * Removing Stars
-      * [Test Remove Starts](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/removing_stars/test_remove_starts.py)
-    * Reverse String
-      * [Test Reverse String](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/stack/reverse_string/test_reverse_string.py)
   * Students And Lunch
     * [Test Students Lunch](https://github.com/BrianLusina/PythonSnips/blob/master/puzzles/students_and_lunch/test_students_lunch.py)
   * Trees
@@ -972,6 +971,10 @@
     * [Test Multiply 5](https://github.com/BrianLusina/PythonSnips/blob/master/pymath/multiply_5/test_multiply_5.py)
   * Perfect Square
     * [Test Perfect Squares](https://github.com/BrianLusina/PythonSnips/blob/master/pymath/perfect_square/test_perfect_squares.py)
+  * Power Of I
+    * [Test Power Of I](https://github.com/BrianLusina/PythonSnips/blob/master/pymath/power_of_i/test_power_of_i.py)
+  * Power Of Two
+    * [Test Power Of Two](https://github.com/BrianLusina/PythonSnips/blob/master/pymath/power_of_two/test_power_of_two.py)
   * Rectangle Area
     * [Test Compute Area](https://github.com/BrianLusina/PythonSnips/blob/master/pymath/rectangle_area/test_compute_area.py)
   * Reverse Integer
@@ -1263,7 +1266,6 @@
     * [Test Plus Minus](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_plus_minus.py)
     * [Test Population Growth](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_population_growth.py)
     * [Test Power Digit Sum](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_power_digit_sum.py)
-    * [Test Power Of I](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_power_of_i.py)
     * [Test Power Of Sum](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_power_of_sum.py)
     * [Test Product Fib](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_product_fib.py)
     * [Test Pythagorean Triplet](https://github.com/BrianLusina/PythonSnips/blob/master/tests/pymath/test_pythagorean_triplet.py)

algorithms/stack/reverse_string/README.md

@@ -0,0 +1,46 @@
+# Reverse String
+
+You are given a character array, s, representing a string. Write a function that reverses the array in-place.
+
+- The reversal must be done by modifying the original array directly.
+- You cannot use extra memory beyond a constant amount O(1).
+
+## Constraints 
+
+- 1 <= `s.length` <= 1000
+- Each `s[i]` is printable ASCII character
+
+## Examples
+
+![Example 1](./images/examples/reverse_string_example_1.png)
+![Example 2](./images/examples/reverse_string_example_2.png)
+![Example 3](./images/examples/reverse_string_example_3.png)
+
+## Solution
+
+As the input is given as a character array, the problem can be solved efficiently by reversing the array in place without
+using extra space for another array. The key idea is that reversing means swapping the first character with the last, the
+second with the second-last, and so on, until all characters are placed in the correct reversed order.
+
+To achieve this, we can use the two pointer technique: one pointer starts at the beginning of the array and the other at
+the end. We swap the characters at each step at these two positions, then move the pointers closer toward the center.
+This continues until the pointers meet or cross, ensuring all characters are reversed.
+
+The steps of the algorithm are as follows:
+
+1. Initialize two pointers: left at the start, and right at the end of the array.
+2. While left < right:
+   - Swap the characters at s[left] and s[right]. 
+   - Increment left by 1 and decrement right by 1 to move the pointers inward.
+3. The process terminates once the left and right pointers meet simultaneously.
+
+### Time Complexity
+
+The solution’s time complexity is O(n), where nnn is the length of the input array, s. Each character in the string is
+swapped at most once as the two pointers move toward the center. As every element is visited at most once, the overall
+time complexity is O(n).
+
+### Space Complexity
+
+The solution’s space complexity is O(1), as the reversal is done in place using only two pointers (left and right). No
+additional data structures are required, regardless of the input size.Thus, the overall space complexity remains O(1).

puzzles/stack/reverse_string/__init__.py → algorithms/stack/reverse_string/__init__.py

@@ -1,3 +1,5 @@
+from typing import List
+
 from datastructures.stacks.dynamic import DynamicSizeStack as Stack
 
 
@@ -29,3 +31,33 @@ def reverse_string(text: str) -> str:
         reversed_string += stack.pop()
 
     return reversed_string
+
+
+def reverse_string_char_array(s: List[str]) -> None:
+    """
+    Reverses a character array in place using two-pointer technique.
+
+    Reference: https://leetcode.com/problems/reverse-string/
+
+    Complexity:
+    Where n is the length of the input list
+    Time: O(n), each character is visited at most once
+    Space: O(1), only two pointers used, no extra data structures
+
+    Args:
+        s (List[str]): character array to reverse in place
+    Returns:
+        None: modifies the input list in place
+    """
+    if not s or len(s) == 1:
+        return
+
+    # Initialize two pointers: left at start, right at end
+    left = 0
+    right = len(s) - 1
+
+    # Swap characters while left is before right
+    while left < right:
+        s[left], s[right] = s[right], s[left]
+        left += 1
+        right -= 1

algorithms/stack/reverse_string/test_reverse_string.py

@@ -0,0 +1,30 @@
+import unittest
+from typing import List
+import copy
+from parameterized import parameterized
+from algorithms.stack.reverse_string import reverse_string, reverse_string_char_array
+
+REVERSE_STRING_CHAR_ARRAY_TEST_CASES = [
+    (["a", "e", "i", "o", "u"], ["u", "o", "i", "e", "a"]),
+    (["A", "l", "e", "x"], ["x", "e", "l", "A"]),
+    (["p", "y", "t", "h", "o", "n"], ["n", "o", "h", "t", "y", "p"]),
+    (["x"], ["x"]),
+]
+
+
+class ReverseStringTestCase(unittest.TestCase):
+    def test_one(self):
+        text = "!evitacudE ot emocleW"
+        actual = reverse_string(text)
+        expected = "Welcome to Educative!"
+        self.assertEqual(expected, actual)
+
+    @parameterized.expand(REVERSE_STRING_CHAR_ARRAY_TEST_CASES)
+    def test_reverse_string_char_array(self, s: List[str], expected: List[str]):
+        s_copy = copy.deepcopy(s)
+        reverse_string_char_array(s_copy)
+        self.assertEqual(expected, s_copy)
+
+
+if __name__ == "__main__":
+    unittest.main()