Question

有人可以向我解释为什么插入排序的方法有误吗？

def insertion_sort(m):
        n = 1
        while n < len(m)-1:
            current_value = m[n]
            if m[n] < m[n-1]:
                m[n] = m[n-1]
                m[n-1] = current_value
            n = n + 1
        return m

#how my code turned out:
m = [7,4,5] returned [4,7,5] instead of [4,5,7]

Answer 1

参见代码注释中的解释：

def insertion_sort(m):
    n = 1
    while n < len(m): # <-- end at the end of the list
        current_value = m[n]
        if m[n] < m[n-1]:
            m[n] = m[n-1]
            m[n-1] = current_value
        n = n + 1
    return m

Answer 2

正如alfasin所提到的，问题在于while循环条件！

您可以在此方案中实际使用for循环。看看this

为了更加pythonic，您可以将两个数字换成a,b = b,a，如@ TigerhawkT3的评论所述！

def insertion_sort(m):
    for n in range(len(m)): #iterate from 0 to m-1. auto increment value is by default 1
            if m[n] < m[n-1]: m[n], m[n-1] = m[n-1], m[n]
    return m

print insertion_sort（[7,4,5]）返回米 print insertion_sort（[7,4,5]）

输出：

[4, 5, 7]

此外，您尝试的那个实际上并不是insertion sort算法。你必须使用超过3个元素来调整你的名单！

Answer 3

评论中的说明

def insertion_sort(array):
    # For each number in the list (not starting 
    # with the first element because the first
    # element has no prior (i.e., no array[j-1])
    for i in range(1, len(array)):
        # Set a temp variable j (totally not necessary
        # but is helpful for the sake of a visual)
        j = i
        # While j is greater than 0 (position 0 is the 
        # very beginning of the array) AND the current 
        # element array[j] is less than the prior element
        # array[j-1] 
        while j>0 and array[j] < array[j-1]:
            # Set the current element equal to the prior 
            # element, and set the prior element equal to
            # the current element (i.e., switch their positions)
            array[j], array[j-1] = array[j-1], array[j]
            # Decrement j (because we are moving each element
            # towards the beginning of the list until it is 
            # in a sorted position)
            j-=1
    return array

 array = [1, 5, 8, 3, 9, 2]

首次for循环迭代：[1,5,8,3,9,2]（5已经处于排序位置）
第二个for循环迭代：[1,5,8,3,9,2]（8已经处于排序位置）
第三：[1,3,5,8,9,2]（将3移回，直至其排序）
第四：[1,2,3,8,9]（移动2，直到它排序）

希望这个小小的插图有所帮助。

这种插入排序方法有什么问题？

3 个答案: