Add quick_sort and 3-way quick_sort with tests

Author: Toshaksha

sorts/quick_sort_with_tests.py

@@ -0,0 +1,81 @@
+from typing import List, Optional
+
+
+def quick_sort(arr: List[int]) -> List[int]:
+    """
+    Classic quick sort implementation using list comprehensions.
+
+    Args:
+        arr (List[int]): List of integers to sort.
+
+    Returns:
+        List[int]: New sorted list.
+    """
+    if len(arr) <= 1:
+        return arr
+    else:
+        pivot = arr[len(arr) // 2]
+        left = [x for x in arr if x < pivot]
+        middle = [x for x in arr if x == pivot]
+        right = [x for x in arr if x > pivot]
+        return quick_sort(left) + middle + quick_sort(right)
+
+
+def quick_sort_3way(arr: List[int], low: int = 0, high: Optional[int] = None) -> List[int]:
+    """
+    In-place 3-way partitioning quick sort.
+
+    Args:
+        arr (List[int]): List of integers to sort.
+        low (int): Starting index of the sublist to sort.
+        high (Optional[int]): Ending index of the sublist to sort.
+
+    Returns:
+        List[int]: The same list sorted in-place.
+    """
+    if high is None:
+        high = len(arr) - 1
+
+    if low < high:
+        lt, gt = low, high
+        pivot = arr[low]
+        i = low + 1
+
+        while i <= gt:
+            if arr[i] < pivot:
+                arr[lt], arr[i] = arr[i], arr[lt]
+                lt += 1
+                i += 1
+            elif arr[i] > pivot:
+                arr[i], arr[gt] = arr[gt], arr[i]
+                gt -= 1
+            else:
+                i += 1
+
+        quick_sort_3way(arr, low, lt - 1)
+        quick_sort_3way(arr, gt + 1, high)
+
+    return arr
+
+
+def test_quick_sorts():
+    """
+    Simple test cases for quick_sort and quick_sort_3way functions.
+    """
+    test_cases = [
+        ([3, 6, 8, 10, 1, 2, 1], [1, 1, 2, 3, 6, 8, 10]),
+        ([4, 5, 4, 3, 4, 2, 1, 4], [1, 2, 3, 4, 4, 4, 4, 5]),
+        ([], []),
+        ([1], [1]),
+        ([2, 1], [1, 2]),
+    ]
+
+    for i, (input_arr, expected) in enumerate(test_cases):
+        assert quick_sort(input_arr) == expected, f"quick_sort failed on test case {i + 1}"
+        assert quick_sort_3way(input_arr.copy()) == expected, f"quick_sort_3way failed on test case {i + 1}"
+
+    print("All tests passed!")
+
+
+if __name__ == "__main__":
+    test_quick_sorts()