Problem Set 2

姓名： 学号：

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• 如果你想修改你的作业，请不要修改生成的txt文件。请重新填写表单然后重新生成txt文件。不要对生成的txt文件做任何操作（修改内容，修改学号，修改姓名）。

1. Write a program to operate a sentence below.

   1
   1
   My email address is wang.lu@mail.shufe.edu.cn It was created on 1st Sept. 2017 Friday
   

   • count the number of letter e in this sentence.

   • show the host of the email address mail.shufe.edu.cn by using find()

   • show the time in a list ['1st', 'Sept.', '2017', 'Friday'] by using find() and split()

2. Write a program to create a dictionary that contains the following information.

   Name	Favorite Language	Age
   Mike	Java	20
   Tracy	C++	21
   Jack	Python	19

   Use for to print the information such that the names are in alphabetical order. The following shows an execution of the program.

   3
   1
   Jack Python 19
   2
   Mike Java 20
   3
   Tracy C++ 21
   

3. Write a program to show the complete multiplication table (九九乘法表). The following shows an execution of the program. (Hint: please use nested for .)

   9
   1
   1*1=1 
   2
   2*1=2 2*2=4 
   3
   3*1=3 3*2=6 3*3=9 
   4
   4*1=4 4*2=8 4*3=12 4*4=16 
   5
   5*1=5 5*2=10 5*3=15 5*4=20 5*5=25 
   6
   6*1=6 6*2=12 6*3=18 6*4=24 6*5=30 6*6=36 
   7
   7*1=7 7*2=14 7*3=21 7*4=28 7*5=35 7*6=42 7*7=49 
   8
   8*1=8 8*2=16 8*3=24 8*4=32 8*5=40 8*6=48 8*7=56 8*8=64 
   9
   9*1=9 9*2=18 9*3=27 9*4=36 9*5=45 9*6=54 9*7=63 9*8=72 9*9=81
   

4. Write a program that creates a function fib(n) to show the Fibonacci sequence. The length of the sequence is n. Fibonacci sequence is a sequence such that every number after the first two is the sum of the two preceding ones. For example, $1,1,2,3,5,8,13,21,34,55,89,...$$1,1,2,3,5,8,13,21,34,55,89,...$ . Note that the third element 2 is the sum of the first two elements, 1+1=2, and the fifth element 5 is the sum of 2 and 3. (8 = 3+5,13=5+8, and so on.) The following shows an execution of the program.

   2
   1
   >>>fib(8)
   2
   1 1 2 3 5 8 13 21
   

   (Hint: you can start with the following incomplete program. )

   14
   1
   def fib(n):
   2
     if n==1:
   3
       print(1)
   4
     elif n==2:
   5
       print(1,1)
   6
     elif n>2:
   7
       print(1,1,end=" ")
   8
     count = 0
   9
     n1 = 1
   10
     n2 = 1
   11
     while count < n-2:
   12
       nth = n1 + n2
   13
       print(nth,end=" ")
   14
           # add your program here to complete it
   

5. Design a function noDuplicates(x) to receive a string and return a new string in which there is no duplicates. The following shows the execution of the function.

   4
   1
   x="aaaaaaaaaa"
   2
   print(noDuplicates(x))
   3
   #output
   4
   a
   

   4
   1
   x="abbcdcefedcba"
   2
   print(noDuplicates(x))
   3
   #output
   4
   abcdef
   

6. Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. The following shows an execution of the function. (Hint: create two functions: one is for finding all the triplets giving the sum of zero, and the other is for deleting duplicates.)

   4
   1
   y=[-1,0,1,2,-1,-4,6,-2]
   2
   print(threeSum(y))
   3
   #output
   4
   [[-1, 0, 1], [-1, -1, 2], [-2, 0, 2], [-4, -2, 6]]
   

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