Python实现快速排序和插入排序算法及自定义排序的示例
一、快速排序
快速排序（Quicksort）是对冒泡排序的一种改进。由C. A. R. Hoare在1962年提出。它的基本思想是：通过一趟排序将要排序的数据分割成独立的两部分，其中一部分的所有数据都比另外一部分的所有数据都要小，然后再按此方法对这两部分数据分别进行快速排序，整个排序过程可以递归进行，以此达到整个数据变成有序序列。
快速排序，递归实现
def quick_sort(num_list):
"""
快速排序
"""
if num_list == []:
return num_list
smallList = []
bigList = []
middleElement = num_list[0]
for i in num_list[1:]:
if i <= middleElement:
smallList.append(i)
else:
bigList.append(i)
return quick_sort(smallList)+[middleElement]+quick_sort(bigList)
二、插入排序
插入排序（Insertion Sort）的算法描述是一种简单直观的排序算法。它的工作原理是通过构建有序序列，对于未排序数据，在已排序序列中从后向前扫描，找到相应位置并插入。插入排序在实现上，通常采用in-place排序（即只需用到O(1)的额外空间的排序），因而在从后向前扫描过程中，需要反复把已排序元素逐步向后挪位，为最新元素提供插入空间。
插入排序
def insert_sort(num_list):
"""
插入排序
"""
for i in range(len(num_list)-1):
for j in range(i+1, len(num_list)):
if num_list[i]>num_list[j]:
num_list[i],num_list[j] = num_list[j],num_list[i]
return num_list
三、自定义排序
利用 sort() 或 sorted() 的 key 即可实现。
示例如下：
def sort_key(obj): sorted_list = [4, 2, 5, 9, 7, 8, 1, 3, 6, 0] return sorted_list.index(obj) if __name__ == '__main__': print sorted(range(10), key=sort_key) # 输出结果如下 [4, 2, 5, 9, 7, 8, 1, 3, 6, 0]
# 利用关键字在列表中的索引位置，进行自定义排序
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