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]

原文地址:https://www.cnblogs.com/gengcx/p/6798950.html