day5冒泡排序
冒泡排序:是一种基础的算法,实现数据的排序,排序的原则是前一个与后一个进行比较,如果前面的值大则交换,否则不交换,多次循环每次把最大的数据循环至后面就能够完成所需。
上面的图是冒泡排序的原理,每次循环把最大的值遍历到最后面,而且循环的过程中,每次循环的次数减1。
下面来看一个实例,我们将一个列表data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6],我们将列表进行排序。代码如下:
首先取出列表的顺序和下表enumerate(
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
for index,i in enumerate(data[0:-1]):
if i > data[index+1]:
data[index+1],data[index] = i,data[index+1]
print(data)
运行如下:
[4, 10, 21, 33, 3, 54, 8, 5, 11, 2, 1, 2, 13, 6, 13]
可以看出是调换了位置,但是是有错误的。13出现了两次,22消失了,这是由于在循环过程中,我们改动了列表的下标,改动下标之后就出现了错误,有些值被替换了。因为不能这样做,或者下面这样也是不行的。
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
for index,i in enumerate(data[0:-1]):
if i > data[index+1]:
#data[index+1],data[index] = i,data[index+1]
#存储一个临时变量用来存储信息
tmp = data[index+1]
data[index+1] = i
data[index] = tmp
print(data)
上面代码中tem的作用是存储一个data[index+1]因为我们知道,要把data[index]和data[index+1]进行交换,如果单纯的交换,有一个会被替换,因为要把被替换的值存在一个新的变量中,这样就避免了这种错误。
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
for j in range(len(data)):
for i in range(len(data)-1):
if data[i] > data[i+1]:
tem = data[i+1]
data[i+1] = data[i]
data[i] = tem
print(data)
运行代码结果如下:
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
上面代码中,我们的思路是循环列表中的每个元素,前一个和后一个进行比较,如果前一个大于后一个就进行替换,否则不动,这样每次把最后一个最大值移到列表的末尾,就能实现功能,列表有多少长度,我们就循环多少次,因此我们在外面加入了for循环,让下面的列表排序能够进行多次比较。但是上面的代码可以有一个改进的地方,我们知道,每次循环都会把一个最大值放到列表的末尾,因此循环的次数可以每次递减1次,下面我们对代码进行改进:
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
for j in range(1,len(data)):
for i in range(len(data)-j):
if data[i] > data[i+1]:
tem = data[i+1]
data[i+1] = data[i]
data[i] = tem
print(data)
运行结果如下:
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
结果是一样的,但是我们这里避免了很多不必要的循环,我们看一下两个代码各自需要循环多少次,为此我们可以定义一个n在里面,每次循环的时候加1。
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
n = 0
for j in range(len(data)):
#for j in range(1,len(data)):
for i in range(len(data)-1):
#for i in range(len(data) - j):
n = n + 1
if data[i] > data[i+1]:
tem = data[i+1]
data[i+1] = data[i]
data[i] = tem
print(n)
print(data)
经过上面两种方法的测试,没有改进的方法运行了210次,改进之后的方法值运行了105次,可见很多时候改进一点点就能节省很多时间。
下面来看看代码每次运行的结果:
[4, 10, 33, 21, 54, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 54, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 54, 8, 11, 5, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 54, 11, 5, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 54, 5, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 54, 22, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 54, 2, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 54, 1, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 1, 54, 17, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 1, 17, 54, 13, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 1, 17, 13, 54, 6]
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 33, 8, 11, 5, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 33, 11, 5, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 33, 5, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 33, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 33, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 33, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 1, 33, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 1, 17, 33, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 1, 17, 13, 33, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 21, 8, 11, 5, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 21, 11, 5, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 21, 5, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 22, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 1, 22, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 1, 17, 22, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 1, 17, 13, 22, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 10, 8, 11, 5, 21, 2, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 11, 5, 21, 2, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 21, 2, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 21, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 1, 21, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 1, 17, 21, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 1, 17, 13, 21, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 1, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 10, 5, 11, 2, 1, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 11, 2, 1, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 2, 11, 1, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 2, 1, 11, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 2, 1, 11, 13, 17, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 2, 1, 11, 13, 6, 17, 21, 22, 33, 54]
[3, 4, 5, 8, 10, 2, 1, 11, 13, 6, 17, 21, 22, 33, 54]
[3, 4, 5, 8, 2, 10, 1, 11, 13, 6, 17, 21, 22, 33, 54]
[3, 4, 5, 8, 2, 1, 10, 11, 13, 6, 17, 21, 22, 33, 54]
[3, 4, 5, 8, 2, 1, 10, 11, 6, 13, 17, 21, 22, 33, 54]
[3, 4, 5, 2, 8, 1, 10, 11, 6, 13, 17, 21, 22, 33, 54]
[3, 4, 5, 2, 1, 8, 10, 11, 6, 13, 17, 21, 22, 33, 54]
[3, 4, 5, 2, 1, 8, 10, 6, 11, 13, 17, 21, 22, 33, 54]
[3, 4, 2, 5, 1, 8, 10, 6, 11, 13, 17, 21, 22, 33, 54]
[3, 4, 2, 1, 5, 8, 10, 6, 11, 13, 17, 21, 22, 33, 54]
[3, 4, 2, 1, 5, 8, 6, 10, 11, 13, 17, 21, 22, 33, 54]
[3, 2, 4, 1, 5, 8, 6, 10, 11, 13, 17, 21, 22, 33, 54]
[3, 2, 1, 4, 5, 8, 6, 10, 11, 13, 17, 21, 22, 33, 54]
[3, 2, 1, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[2, 3, 1, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[2, 1, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
上面是分布每次运行的情况,下面是没一大步运行的情况:
[4, 10, 21, 33, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6, 54]
[4, 10, 21, 3, 8, 11, 5, 22, 2, 1, 17, 13, 6, 33, 54]
[4, 10, 3, 8, 11, 5, 21, 2, 1, 17, 13, 6, 22, 33, 54]
[4, 3, 8, 10, 5, 11, 2, 1, 17, 13, 6, 21, 22, 33, 54]
[3, 4, 8, 5, 10, 2, 1, 11, 13, 6, 17, 21, 22, 33, 54]
[3, 4, 5, 8, 2, 1, 10, 11, 6, 13, 17, 21, 22, 33, 54]
[3, 4, 5, 2, 1, 8, 10, 6, 11, 13, 17, 21, 22, 33, 54]
[3, 4, 2, 1, 5, 8, 6, 10, 11, 13, 17, 21, 22, 33, 54]
[3, 2, 1, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[2, 1, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]
当然还有一种简单的方法能够实现列表的排序,而且只需要循环列表长度的次数即可:
data = [10,4,33,21,54,3,8,11,5,22,2,1,17,13,6]
numbers = []
#查找列表中最小值的位置
for i in range(len(data)):
num = data.pop(data.index(min(data)))
numbers.append(num)
print(numbers)
方法的原理是,我们知道,目的是实现列表中元素的排序,那么我们每次找到列表中的最小值并且把这个最小值使用pop方法弹出来,那么列表的长度每次减1,我们每次都只找最小值,使用index()查找值的索引,使用另外一个列表去接收。就能够实现,运行结果如下:
[1, 2, 3, 4, 5, 6, 8, 10, 11, 13, 17, 21, 22, 33, 54]