Lecture "Brute-force argorithms", exercise 5

[essepuntato]

Write in Python the function def my_reversed(input_list), which behave like the built-in function reversed() introduced in Section "Insertion sort" and returns a proper list, and accompany the function with the related test case. It is not possible to use the built-in function reversed() in the implementation.

[ghasempouri1984]

unlike reversed(), with [::-1] code reverse the list without modifying it:

def test_my_reversed(input_list, expected):
    result = my_reversed(input_list)
    if expected == result:
        return True
    else:
        return False

def my_reversed(input_list):
    reversed_list = input_list[::-1]
    return reversed_list

print(test_my_reversed([], []))
print(test_my_reversed([1], [1]))
print(test_my_reversed([1, 2, 3, 4], [4, 3, 2, 1]))
print(test_my_reversed([1, 2, 3, 4, "5", " ", 7], [7, " ", "5", 4, 3, 2, 1]))

[RebeccaJillianBeattie]

[federicabonifazi]

[CarmenSantaniello]

Reverse with slicing:

def test_my_reversed(input_list, expected):
    result = my_reversed(input_list)
    if expected == result:
        return True
    else:
        return False

def my_reversed(input_list):
    output_list = input_list[::-1]
    return output_list

my_list = [0, 1, 2, 3, 4, 5]

print(test_my_reversed(my_list, [5, 4, 3, 2, 1, 0]))
print(my_reversed(my_list))

It returns:

True 
[5, 4, 3, 2, 1, 0]

[11051620]

def my_reversed(input_list):

my_stack = deque()

for item in input_list:
    my_stack.appendleft(item)

return my_stack

[olgagolgan]

[martasoricetti]

[ManueleVeggi]

#Test code for the algorithm
def test_my_reverse(input_list, expected_reverse):
    result = my_reverse(input_list)
    if result == expected_reverse:
        return True
    else:
        return False

#Code for the algorithm
def my_reverse (input_list):
    olist = list()
    while len(input_list) > 0:
        item = input_list[-1]
        olist.append(item)
        del input_list[-1]
    return olist

#Some of the possible tests
print(test_my_reverse(["a", "b", "c", "d"], ["d", "c", "b", "a"])) # N. 1, expect: T
print(test_my_reverse(["a", "b", "c", "d"], ["d", "b", "c", "a"])) # N. 2, expect: F
print(test_my_reverse(["a", "b", "c", "d"], ["a", "b", "c", "d"])) # N. 3, expect: F
print(test_my_reverse(["a", "b", "c", "d"], ["a", "b", "c"]))        # N. 4, expect: F
print(test_my_reverse(["a", "b", "c", "d"], ["a", "a", "c", "d"])) # N. 5, expect: F

If code is run, the results coincide with our expectations: therefore the code should be correct

[tommasobattisti]

def test_my_reversed(input_list2, expected):
    result = my_reversed(input_list2)
    if result == expected:
        return True
    else:
        return False

def my_reversed(input_list2):
    output_p_list2 = []
    while len(input_list2) > 0:
        output_p_list2.append(input_list2.pop())
    return output_p_list2

print(test_my_reversed([1, 2, 3, 4, 5], [5, 4, 3, 2, 1]))
print(test_my_reversed(['a', 'b', 'c', 'd', 'e'], ['e', 'd', 'c', 'b', 'a']))

[katya-avem]

[OrsolaMBorrini]

def test_my_reversed(input_list,expected):
    my_result = my_reversed(input_list)
    if my_result == expected:
        return True
    else:
        return False

def my_reversed(input_list):
    output_list = list()
    for item in input_list:
        output_list.insert(0,item)
    return output_list

example_list = [0,1,2]
print(test_my_reversed(example_list,[2,1,0])) #This should return True
print(my_reversed(["A","B","D","K","C"]))

[chloeppd]

[MaddaGh]

[AnastasiyaSopyryaeva]

Task_5

def testing(input_list, expected):
    result = my_reversed(input_list)
    if result == expected:
        return True
    else:
        return False

def my_reversed(input_list):
    output = []
    number = 0
    maxnumber = len(input_list)
    while number < maxnumber:
        output.append(input_list.pop()) 
        number +=1
    return output

print(testing([0, 1, 2], [2, 1, 0]))
print(testing([0, 1, 2, 5, 6], [2, 1, 0]))

Returns True False

[angstigone]

[essepuntato]

Hi all,

Several different approaches were used, that's wonderful indeed! Just a few comments:

• Try to run your code using the following list, and see if your function continues to work as expected: [1, 2, 3, 1]
• As an additional exercise for all of you, try to run the code you wrote with Python Tutor, and observe what happens to the various object involved in the execution of your code – we will clarify better some peculiar aspects related to lists and other objects in a few lectures anyway

[AmeliaLamargese]

def test_my_reversed(input_list, expected):
    result = my_reversed(input_list)
    if result == expected:
        return True
    else: 
        return False

def my_reversed(input_list):
    output_list = list()
    position = len(input_list) -1
    while position >= 0:
        output_list.append(input_list[position])
        position -= 1

    return output_list

print(test_my_reversed([], []))
print(test_my_reversed([1, 2, 3], [3, 2, 1]))
print(test_my_reversed(["ciao", "hello", "salut"], ["salut", "hello", "ciao"]))
print(test_my_reversed(["ciao", 1, "hello", 2], [2, "hello", 1, "ciao"]))

[sarabecchi]

def my_reversed(input_list):
    l = list()
    for item in input_list:
        l.insert(0, item)
    return l

list_1 = [1, 2, 3, 4, 5, 6, 7, 8]
print(my_reversed(list_1))

def test_my_reversed(input_list, expected):
    result = my_reversed(input_list)
    if result == expected:
        return True
    else:
        return False

print(test_my_reversed([1, 2, 3], [3, 2, 1]))
print(test_my_reversed([3, 2, 1], [1, 2, 3]))
print(test_my_reversed(["a", "b", "c"], ["c", "b", "a"]))
print(test_my_reversed(["c", "b", "a"], ["a", "b", "c"]))
print(test_my_reversed([], []))

OUTPUT:

[8, 7, 6, 5, 4, 3, 2, 1]
True
True
True
True
True