python算法之排序算法

Posted 2020-10-22 liuyankui163

冒泡排序

 1 def bubble_sort(li):
 2     ‘‘‘本算法复杂度为O(n**2)‘‘‘
 3     for i in range(len(li)-1):# 列表长度为n，需要n-1趟
 4         ‘‘‘
 5         i的取值个数为n-1
 6         i=0时，j的取值个数为n-1
 7         i=1时，j的取值个数为n-1-1
 8         i=2时，j的取值个数为n-1-1-1
 9         故对于i，j的取值个数为n-1-
10         ‘‘‘
11         for j in range(len(li)-1-i):
12             # 若后面的数小于前面数，则两数前后交换
13             if li[j] > li[j+1]:
14                 li[j],li[j+1] = li[j+1],li[j]
15 li = [random.randint(0,10000) for i in range(10000)]
16 print(li)
17 bubble_sort(li)
18 print(li)

选择排序

# 选择排序
# 一趟排序记录最小的数，放到第一个位置
# 再一趟排序记录记录无序区最小的数，放到第二个位置
# ......
# 算法关键的：有序区和无序区，无序去最小数的位置
# 本算法复杂度为O(n**2)
def select_sort(li):
    for i in range(len(li)-1):
        # 需要排n-1趟
        tmp = i # tmp用来记录无序区最小的数的索引
        for j in range(i+1,len(li)):
            ‘‘‘
            j的范围即无序区范围
            i=0时，j的范围是1到最后
            i=1时，j的范围是2到最后
            ......
            ‘‘‘
            if li[j]<li[tmp]:
                tmp=j
        li[i],li[tmp] = li[tmp],li[i]
# li = [23,35,3,23,23,2,1,4,34,23,4,3,23,5,23,2,34,23,23,2,34,2,4534,6,7,4,6,8,3,42]
# li = [random.randint(0,10000) for i in range(1000)]
# print(len(li),li)
# select_sort(li) # 用时0.053
# print(li)

# li = [random.randint(0,10000) for i in range(10000)]
# print(len(li),li)
# select_sort(li) # 用时6.057
# print(li)

 插入排序

 本算法时间复杂度也是O(n**2)

 1 def insert_sort(li):
 2     for i in range(1,len(li)):
 3         tmp = li[i]
 4         j = i-1# j指手里的牌的下标
 5         while j>=0 and li[j] > tmp:
 6             li[j+1] = li[j]
 7             j -= 1
 8         li[j+1] = tmp
 9 # li = [3,2,5,6,4,3,6,7,5,7,6,45,7,8,8,34]
10 # print(insert_sort(li))
11 li = [random.randint(0,10000) for i in range(1000)]
12 print(li)
13 insert_sort(li)# 0.049
14 print(li)#
15 
16 li = [random.randint(0,10000) for i in range(10000)]
17 print(li)
18 insert_sort(li)# 5.46
19 print(li)#