Python课程学习记录_15周作业

• 实现下列函数，并将其定义为模块insert, 即存储在insert.py中：
  def insert(aList, i):

  """aList[0:i] are in ascending order,

  i.e. aList[0] <= aList[1]<= ... <= aList[i-1].

  insert(aList, i) will insert aList[i] into proper postion and

  make aList[0:i+1] in asceding order and aList[i+1:] unchanged.

  """

  def insert(aList, i):
  	key=aList[i]
  	j=i-1
  	while j>=0 and aList[j] > key:
  		aList[j+1]=aList[j]
  		j-=1
  	aList[j+1]=key
  	return aList

  这里主要实现一个插入排序
• 二. 请使用递归实现以下函数，并将其定义为模块seqrec, 即存储在seqrec.py中。

  def seq_rec(n):

  """Return the nth term of the sequence defined by a₀=1, a₁=2,a₂ = 2, a_n = a_n-1+a_n-2+a_n-3,

  _{i.e., seq_rec(n) returns an.}

  _"""

  def seq_rec(n):
  	if n == 0: 
  		return 1
  	elif n == 1 or n == 2:
  		return 2
  	else:
  		return seq_rec(n-1)+seq_rec(n-2)+seq_rec(n-3)

  
  

  三. 请使用迭代（非递归）实现以下函数，并将其定义为模块seqiter, 即存储在seqiter.py中。

  def seq_iter(n):

  """Return the nth term of the sequence defined by a₀=1, a₁=2,a₂ = 2, a_n = a_n-1+a_n-2+a_n-3,

  _{i.e., seq_iter(n) returns an.}

  _"""实现

  def seq_iter(n):
  	a=[1,2,2]
  	if n == 0: 
  		return a[0]
  	elif n == 1 or n == 2:
  		return a[1]
  	else:
  		i=3
  		for i in range(3,n+1):
  			temp=a[i-1]+a[i-2]+a[i-3]
  			a.append(temp)
  		return a[n]