冒泡排序作业 [英] Bubble Sort Homework

问题描述

在课堂上，我们正在做排序算法，虽然我知道他们很好，当谈到他们和书面的伪code，我有写实际code为他们的问题。

In class we are doing sorting algorithms and, although I understand them fine when talking about them and writing pseudocode, I am having problems writing actual code for them.

这是我在Python的尝试：

This is my attempt in Python:

mylist = [12, 5, 13, 8, 9, 65]

def bubble(badList):
    length = len(badList) - 1
    unsorted = True

    while unsorted:
    	for element in range(0,length):
		    unsorted = False
		    if badList[element] > badList[element + 1]:
			    hold = badList[element + 1]
			    badList[element + 1] = badList[element]
			    badList[element] = hold
			    print badList
		    else:
			    unsorted = True

print bubble(mylist)

现在，这个（据我可以告诉）排序正确的，但一旦它完成它只是循环下去。

Now, this (as far as I can tell) sorts correctly, but once it finishes it just loops indefinitely.

这怎么code是固定的，因此函数完成正常和正确排序任何（合理的）尺寸的列表？

How can this code be fixed so the function finishes properly and correctly sorts a list of any (reasonable) size?

P.S。我知道，我真的不应该有打印的功能，我应该有回报，但我没有这样做还因为我的code并没有真正的工作还没有。

P.S. I know I should not really have prints in a function and I should have a return, but I just have not done that yet as my code does not really work yet.

推荐答案

要解释为什么你的脚本不能正常工作，现在，我要重命名变量未分类来排序。

To explain why your script isn't working right now, I'll rename the variable unsorted to sorted.

首先，你的名单尚未排序。当然，我们设置排序到假。

At first, your list isn't yet sorted. Of course, we set sorted to False.

一旦我们开始了，而循环中，我们假设该列表已经排序。我们的想法是这样的：只要我们发现两个元素是不是在正确的顺序，我们设置排序返回假。 排序仍将真的只是，如果有错误的顺序没有元素的。

As soon as we start the while loop, we assume that the list is already sorted. The idea is this: as soon as we find two elements that are not in the right order, we set sorted back to False. sorted will remain True only if there were no elements in the wrong order.

sorted = False  # We haven't started sorting yet

while not sorted:
    sorted = True  # Assume the list is now sorted
    for element in range(0, length):
        if badList[element] > badList[element + 1]:
            sorted = False  # We found two elements in the wrong order
            hold = badList[element + 1]
            badList[element + 1] = badList[element]
            badList[element] = hold
    # We went through the whole list. At this point, if there were no elements
    # in the wrong order, sorted is still True. Otherwise, it's false, and the
    # while loop executes again.

也有轻微的小问题，这将有助于在code更有效和可读性。

There are also minor little issues that would help the code be more efficient or readable.

• 在为循环，可以使用变量元素。从技术上来说，元素不是一个元素;这是一些重presenting一个列表索引。此外，这是相当长的。在这种情况下，只需使用一个临时变量的名称，如我为指数。

• In the for loop, you use the variable element. Technically, element is not an element; it's a number representing a list index. Also, it's quite long. In these cases, just use a temporary variable name, like i for "index".

for i in range(0, length):

在范围命令也可以只有一个参数（名为停止）。在这种情况下，你的所有整数列表从0到这样的说法。

The range command can also take just one argument (named stop). In that case, you get a list of all the integers from 0 to that argument.

for i in range(length):

建议变量小写用下划线被命名为 Python的风格指南。这是一个非常小的鸡蛋里挑骨头一点点这样的脚本;它更让你习惯什么的Python code最常类似。

The Python Style Guide recommends that variables be named in lowercase with underscores. This is a very minor nitpick for a little script like this; it's more to get you accustomed to what Python code most often resembles.

def bubble(bad_list):

要交换两个变量的值，给他们写一个元组分配。右手边被评价为一个元组（例如，（badList [I + 1]，badList [I]）是（3,5） ），然后被分配到左侧的两个变量（（badList [I]，badList [I + 1]））。

To swap the values of two variables, write them as a tuple assignment. The right hand side gets evaluated as a tuple (say, (badList[i+1], badList[i]) is (3, 5)) and then gets assigned to the two variables on the left hand side ((badList[i], badList[i+1])).

bad_list[i], bad_list[i+1] = bad_list[i+1], bad_list[i]

把它放在一起，你会得到这样的：

Put it all together, and you get this:

my_list = [12, 5, 13, 8, 9, 65]

def bubble(bad_list):
    length = len(bad_list) - 1
    sorted = False

    while not sorted:
        sorted = True
        for i in range(length):
            if bad_list[i] > bad_list[i+1]:
                sorted = False
                bad_list[i], bad_list[i+1] = bad_list[i+1], bad_list[i]

bubble(my_list)
print my_list

（我删除了您的打印语句也顺便说一句。）

(I removed your print statement too, by the way.)

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