Question

我正在尝试编写“快速排序”算法的python脚本。

这是我的代码：

def quick_sort(sequence):
    pivot = sequence.pop()
    greater =[]
    lower = []

    for i in sequence:
            if sequence[i] > pivot : 
                greater.append(sequence[i])
            else:
                lower.append(sequence[i])
    return lower + pivot + greater 

sequence = [1,6,3,5,9,6,0,9,3,5,12,37,33,65,55,454,45,len("good")]
quick_sort(sequence)

但是我得到一个错误：

Traceback (most recent call last):
  File "<string>", line 14, in <module>
  File "<string>", line 7, in quick_sort
IndexError: list index out of range

请有人可以帮助我解决该错误吗？

Answer 1

根据评论，这个问题只想对列表进行排序。这很简单。要么这样做：

lst = sorted(lst)

或者，如果您不想使用等号运算符：

lst.sort()

将自动对其进行排序。

Answer 2

问题出在这两行：

        for i in sequence:
            if sequence[i] > pivot :

在Python中，for x in _list将遍历_list的值，而不是索引。在您的示例中，这意味着在某个时刻i == 37和if条件尝试访问超出范围的sequence[37]。有两种方法可以解决此问题：

for i in range(len(sequence)):将为您提供索引。
仅使用i的值，而不是将其用作索引（也在您添加的行中）。就我个人而言，这是我的偏爱-总体而言，它看起来更整洁。

此外，请注意，lower和greater是列表，而pivot是整数，因此您无法做lower + pivot + greater-您必须包装{ {1}}在列表的首位（pivot）。

Answer 3

这是我前一段时间实现的“快速排序”，可能会帮助您设计和测试自己的“快速排序”算法：

import random
from typing import TypeVar, List
from scipy import stats

T = TypeVar('T')


def quick_sort(input_list: List[T]) -> List[T]:
    """"
    Returns an ascending sorted list;
    Input variable is an integer or float array;
    Theoretical Complexity: O(N*Log N) Time and O(N) Memory
    """

    sort(input_list, 0, len(input_list) - 1)
    return input_list


def sort(input_list: List[T], start_index: int, end_index: int) -> None:
    """Recursively sorts the two pivot-divided sublists;"""
    if start_index >= end_index:
        return
    pivot_index = partition(input_list, start_index, end_index)
    sort(input_list, start_index, pivot_index - 1)
    sort(input_list, pivot_index + 1, end_index)


def partition(input_list: List[T], start_index: int, end_index: int) -> int:
    """
    Returns the end index; Partitions a list into two sublists;
    """
    pivot = input_list[start_index]

    i, j = start_index + 1, end_index

    while i <= j:
        while input_list[i] < pivot and i < end_index:
            i += 1
        while input_list[j] > pivot:
            j -= 1

        if i < j:
            temp = input_list[i]
            input_list[i] = input_list[j]
            input_list[j] = temp
            i += 1
            j -= 1
        else:
            break

    input_list[start_index] = input_list[j]
    input_list[j] = pivot

    return j


if __name__ == "__main__":

    # Creates a dash line string and a new line for in between the tests.
    delimiter = "-" * 70 + "\n"

    # Generates a random integer list.
    test_list_integer = random.sample(range(-100, 100), 15) * 3
    print(f"""The unsorted integer array is:
        {test_list_integer}""")
    print(delimiter)

    # Generates a random float list.
    test_list_float = stats.uniform(0, 100).rvs(45)
    print(f"""The unsorted float array is:
        {test_list_float}""")
    print(delimiter)

    # Sample float/integer test list for input.
    integer_float_input = list(test_list_integer + test_list_float)

    # Sample float/integer test list for output.
    integer_float_output = sorted(integer_float_input)

    sorting_algorithms = [
        ("Quick Sort", quick_sort)
    ]

    # Testing
    for description, func in sorting_algorithms:
        if (func(integer_float_input.copy()) == integer_float_output):
            print(f"{description} Test was Successful.")
        else:
            print(f"{description} Test was not Successful.")
        print(f"""{description} (Integer):
            {func(test_list_integer.copy())}""")
        print(f"""{description} (Float):
            {func(test_list_float.copy())}""")
        print(delimiter)

打印

The unsorted integer array is:
        [-37, 74, -9, 58, 96, 82, 32, 94, -77, -54, -13, -10, -82, 57, 6, -37, 74, -9, 58, 96, 82, 32, 94, -77, -54, -13, -10, -82, 57, 6, -37, 74, -9, 58, 96, 82, 32, 94, -77, -54, -13, -10, -82, 57, 6]
----------------------------------------------------------------------

The unsorted float array is:
        [ 4.46747765 21.96382498 21.00086463 49.15870339 95.19971828 94.5108942
  1.88156027 49.1355604  78.5032007  32.4662292  15.0415828  75.04492651
 29.491373    4.02412264 22.34068707 97.39317437 27.64026964 85.52244153
  0.53119133 16.63664738 86.79522363 33.07979585 88.50108333 57.40225507
 72.25826399 99.82793291 99.84493522 15.96858729 33.58735178  1.70611819
 68.07308792 46.09522364 21.42563941  5.55154387 10.60707898 92.78939519
 77.01866529 14.12783987 87.17625745 52.8310454  19.39884535 94.30883322
 96.14062517 45.56022192 24.39705178]
----------------------------------------------------------------------

Quick Sort Test was Successful.
Quick Sort (Integer):
            [-82, -82, -82, -77, -77, -77, -54, -54, -54, -37, -37, -37, -13, -13, -13, -10, -10, -10, -9, -9, -9, 6, 6, 6, 32, 32, 32, 57, 57, 57, 58, 58, 58, 74, 74, 74, 82, 82, 82, 94, 94, 94, 96, 96, 96]
Quick Sort (Float):
            [ 0.53119133  1.70611819  1.88156027  4.02412264  4.46747765  5.55154387
 10.60707898 14.12783987 15.0415828  15.96858729 16.63664738 19.39884535
 21.00086463 21.42563941 21.96382498 22.34068707 24.39705178 27.64026964
 29.491373   32.4662292  33.07979585 33.58735178 45.56022192 46.09522364
 49.1355604  49.15870339 52.8310454  57.40225507 68.07308792 72.25826399
 75.04492651 77.01866529 78.5032007  85.52244153 86.79522363 87.17625745
 88.50108333 92.78939519 94.30883322 94.5108942  95.19971828 96.14062517
 97.39317437 99.82793291 99.84493522]
----------------------------------------------------------------------

参考

Quick Sort Algorithm (Python)

code review of the implementation很好。

IndexError：快速排序算法中的列表索引超出范围

3 个答案:

打印

参考