Merge pull request #199 from Pradeepsingh61/add-python-quick-sort

Add Quick Sort implementation in Pytho

Author: Pradeepsingh61

Python/algorithms/sorting/quick_sort.py

@@ -0,0 +1,103 @@
+"""
+Quick Sort Algorithm
+Time Complexity: O(n log n) average, O(n²) worst case
+Space Complexity: O(log n) due to recursion stack
+Author: Karanjot Singh
+Date: October 2025
+Hacktoberfest 2025
+"""
+
+def partition(arr, low, high):
+    """
+    Partition function for quick sort
+    Places pivot element at correct position and arranges smaller elements to left
+    and greater elements to right of pivot
+
+    Args:
+        arr: List to partition
+        low: Starting index
+        high: Ending index
+
+    Returns:
+        Partition index
+    """
+    pivot = arr[high]
+    i = low - 1
+
+    for j in range(low, high):
+        if arr[j] <= pivot:
+            i += 1
+            arr[i], arr[j] = arr[j], arr[i]
+
+    arr[i + 1], arr[high] = arr[high], arr[i + 1]
+    return i + 1
+
+
+def quick_sort(arr, low=0, high=None):
+    """
+    Quick sort implementation using divide and conquer
+
+    Args:
+        arr: List to sort
+        low: Starting index (default 0)
+        high: Ending index (default None, uses len(arr)-1)
+    """
+    if high is None:
+        high = len(arr) - 1
+
+    if low < high:
+        pi = partition(arr, low, high)
+        quick_sort(arr, low, pi - 1)
+        quick_sort(arr, pi + 1, high)
+
+
+def quick_sort_wrapper(arr):
+    """
+    Wrapper function that returns sorted array
+
+    Args:
+        arr: List to sort
+
+    Returns:
+        Sorted list
+    """
+    arr_copy = arr.copy()
+    quick_sort(arr_copy)
+    return arr_copy
+
+
+# Test cases
+if __name__ == "__main__":
+    print("=== Quick Sort Algorithm ===\n")
+
+    # Test case 1: Random array
+    test1 = [64, 34, 25, 12, 22, 11, 90]
+    print(f"Original array: {test1}")
+    sorted1 = quick_sort_wrapper(test1)
+    print(f"Sorted array:   {sorted1}")
+
+    # Test case 2: Already sorted
+    test2 = [1, 2, 3, 4, 5]
+    print(f"\nOriginal array: {test2}")
+    sorted2 = quick_sort_wrapper(test2)
+    print(f"Sorted array:   {sorted2}")
+
+    # Test case 3: Reverse sorted
+    test3 = [9, 7, 5, 3, 1]
+    print(f"\nOriginal array: {test3}")
+    sorted3 = quick_sort_wrapper(test3)
+    print(f"Sorted array:   {sorted3}")
+
+    # Test case 4: Array with duplicates
+    test4 = [5, 2, 8, 2, 9, 1, 5]
+    print(f"\nOriginal array: {test4}")
+    sorted4 = quick_sort_wrapper(test4)
+    print(f"Sorted array:   {sorted4}")
+
+    # Test case 5: Single element
+    test5 = [42]
+    print(f"\nOriginal array: {test5}")
+    sorted5 = quick_sort_wrapper(test5)
+    print(f"Sorted array:   {sorted5}")
+
+    print("\n✅ All test cases completed!")