快速排序-边缘情况下三个的中位数

def quick_sort(arr):
    if len(arr) <= 1:
        return arr
    elif len(arr) == 2:
        if arr[0] > arr[1]:
            arr[0], arr[1] = arr[1], arr[0]
        return arr
    else:
        # Find the median of the first, middle and last element
        median = get_median(arr[0], arr[len(arr)//2], arr[len(arr)-1])
        
        # Partition the array based on the median
        left = [x for x in arr if x < median]
        middle = [x for x in arr if x == median]
        right = [x for x in arr if x > median]
        
        # Recursively sort the sub-arrays
        return quick_sort(left) + middle + quick_sort(right)

def get_median(a, b, c):
    if a <= b <= c or c <= b <= a:
        return b
    elif b <= a <= c or c <= a <= b:
        return a
    else:
        return c

# Test the algorithm
arr = [9, 5, 2]
sorted_arr = quick_sort(arr)
print(sorted_arr)  # Output: [2, 5, 9]