Python实现快速排序--记录

快速排序的思路是：先从数集中取出一个数字a，将其他所有的数字只要大于a的放到右边，只要小于a的放到左边；这样重复两边的操作，最后完成完全排序。

下面是学习过程中的代码（引用博客https://blog.csdn.net/razor87/article/details/71155518），我用自己的电脑试验了三种方式的排序；我想试验一下三种方法哪种需要的时间少，没试之前认为第一种方法会用的时间比较多，因为它总是在创建list，但是出乎意料，第一种方法所用时间最少；看来代码简洁同时又用时最少的还是比较好。

import numpy as np
import copy
import time
import matplotlib.pyplot as plt

size_list = range(2,100002,1000)
aa = {str(x):np.random.randint(0,x,x) for x in size_list}
a = copy.deepcopy(aa)
a1 = copy.deepcopy(aa)

#===============================================================================
quick_sort1 = lambda array: array if len(array) <= 1 else \
                quick_sort1([item for item in array[1:] if item <= array[0]]) + \
                [array[0]] + \
                quick_sort1([item for item in array[1:] if item > array[0]])

sort1_time = []
for x in size_list:
    start_time1 = time.time()
    b = quick_sort1(aa[str(x)])
    end_time1 = time.time()
    sort1_time.append(end_time1-start_time1)
print('quicksort1 using time:',sort1_time)
#===============================================================================
def quick_sort2(array, left, right):
    if left >= right:
        return
    low = left
    high = right
    key = array[low]
    while left < right:
        while left < right and array[right] > key:
            right -= 1
        array[left] = array[right]
        while left < right and array[left] <= key:
            left += 1
        array[right] = array[left]
    array[right] = key
    quick_sort2(array, low, left - 1)
    quick_sort2(array, left + 1, high)

sort2_time = []
for x in size_list:
    start_time1 = time.time()
    quick_sort2(a[str(x)],0,x-1)
    end_time1 = time.time()
    sort2_time.append(end_time1-start_time1)
print('quicksort2 using time:',sort1_time)
#===============================================================================

def quick_sort3(array, l, r):
    if l < r:
        q = partition(array, l, r)
        quick_sort3(array, l, q - 1)
        quick_sort3(array, q + 1, r)

def partition(array, l, r):
    x = array[r]
    i = l - 1
    for j in range(l, r):
        if array[j] <= x:
            i += 1
            array[i], array[j] = array[j], array[i]
    array[i + 1], array[r] = array[r], array[i+1]
    return i + 1


sort3_time = []
for x in size_list:
    start_time1 = time.time()
    quick_sort3(a1[str(x)],0,x-1)
    end_time1 = time.time()
    sort3_time.append(end_time1-start_time1)
print('quicksort3 using time:',sort1_time)
#===============================================================================

plt.figure()
lable_line = ['method1','method2','method3']
plt.plot(sort1_time)
plt.plot(sort2_time)
plt.plot(sort3_time)
plt.legend(lable_line)

结果：