# CS-UY 1114 Introduction to Programming and Problem Solving  Homework # 9 solved

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Question 1:
Implement function max_abs_val(lst), which returns the maximum absolute
value in lst.
For example, given a list lst [-19, -3, 20, -1, 0, -25], the function should return 25.
Question 2:
Write a function find_all(lst, val), which returns a list containing indices
of the occurrences of val in lst.
For example, given a list lst [‘a’, ‘b’, 10, ‘bb’, ‘a’] and val ‘a’, the function should return
a list [0, 4].
Question 3:
Implement following functions.
a. reverse1(lst)
This function creates a new list containing the elements of lst in reverse order and
returns it..
b. reverse2(lst)
It changes the order of the elements in lst (in place) to be in the reverse order.
Hint: think about the how the positions change before and after the reverse.
You may use the following main program to check your implementation of
reverse1 and reserse2.
def main_q3():
lst1 = [1, 2, 3, 4, 5, 6]
rev_lst1 = reverse1(lst1)
print(”After reverse1, lst1 is ”, lst1, ” and the returned
list is ”, rev_lst1)
lst2 = [1, 2, 3, 4, 5, 6]
reverse2(lst2)
print(”After reverse2, lst2 is ”, lst2)
Expect output:
After recerse1, lst1 is [1, 2, 3, 4, 5, 6] and the returned list
is [6, 5, 4, 3, 2, 1]
After reverse2, lst2 is [6, 5, 4, 3, 2, 1]
Question 4:
Design and implement functions to perform run length encoding of strings.
https://en.wikipedia.org/wiki/Run-length_encoding
a. Run length string encoder. The encoder should take a string, and return the
encoded string in a list.
For example, if given string ”aadccccaa”, after encoding it becomes: [[’a’, 2], [’d’, 1],
[’c’, 4], [’a’, 2]].
b. Run length string decoder. The decoder should take an encoded string (in a list),
and returns the original string.
For example, if given an encoding [[’a’, 2], [’d’, 1], [’c’, 4], [’a’, 2]], the decoded string
Hint: carefully design your functions. If any of your functions seem to be too
complex, you may want to write some ‘helper’ functions that solves some part of
Optional questions for practice:
Question 5:
Write a function add_list( lst1, lst2) that takes two lists of numbers of the
same length and returns a list consisting of the sum of the first numbers, the sum of
the second numbers, etc.
For example add_list([1,2,3], [4,5,6]) should return the list [5, 7, 9]
since 1+ 4 == 5, 2 + 5 == 7, etc.
Your main program should prompt user for input. It should read a list of numbers,
one number per line, followed by “done”, then another list of numbers, one per line,
followed by done. If the lists have different lengths, your main program should print
“Lists are different lengths.” If they are the same length, the main program should
call add_list and print the resulting list, one number per line.
Note: you may define additional ‘helper’ functions in your program.
Question 6:
Implement the function create_prefix_lists(lst) that will return a sequence of lists,
each containing a prefix of lst. All of the lists should be collected as one big list. For
example for [2,4,6,8,10] the function should return [[], [2], [2,4], [2,4,6], [2,4,6,8],
[2,4,6,8,10]]
The challenge:
Question 7:
Write a function to check if a given lsit is a valid Sudoku board. Sudoku:
https://en.wikipedia.org/wiki/Sudoku
You may test your program with the following two lists:
board1 = [
[5,3,4,6,7,8,9,1,2],
[6,7,2,1,9,5,3,4,8],
[1,9,8,3,4,2,5,6,7],
[8,5,9,7,6,1,4,2,3],
[4,2,6,8,5,3,7,9,1],
[7,1,3,9,2,4,8,5,6],
[9,6,1,5,3,7,2,8,4],
[2,8,7,4,1,9,6,3,5],
[3,4,5,2,8,6,1,7,9]
]
board2 = [
[5,3,4,6,7,8,9,1,2],
[6,7,2,1,9,5,3,4,8],
[1,9,8,3,4,2,5,9,7],
[8,5,9,7,6,1,4,2,3],
[4,3,6,8,5,3,7,9,1],
[7,1,3,9,2,4,8,5,6],
[9,6,1,5,3,7,2,8,4],
[2,8,9,4,1,9,6,3,5],
[3,4,5,2,8,6,1,7,9]
]