4. Say Digit

In [21]:

def say_digit(n, mapping):
    """
    Example of head recursion

    5321 -> Five Three Two One
    """

    # 1. Base case
    # when the number is over, 0 is left
    # if you reach 0, return 0
    if n == 0:
        return 0

    # 2. Processing
    # extract the last digit
    digit = n % 10

    # 3. Recurrence relation
    # remove the last digit from the original number
    # till it is reduced to 0
    n = say_digit(n // 10, mapping)

    # when you hit the base case
    # that is when this print statement will be called
    # for the first time
    print(mapping[digit])

def say_digit(n, mapping): """ Example of head recursion 5321 -> Five Three Two One """ # 1. Base case # when the number is over, 0 is left # if you reach 0, return 0 if n == 0: return 0 # 2. Processing # extract the last digit digit = n % 10 # 3. Recurrence relation # remove the last digit from the original number # till it is reduced to 0 n = say_digit(n // 10, mapping) # when you hit the base case # that is when this print statement will be called # for the first time print(mapping[digit])

In [22]:

mapping = {
    0: "zero",
    1: "one",
    2: "two",
    3: "three",
    4: "four",
    5: "five",
    6: "six",
    7: "seven",
    8: "eight",
    9: "nine",
}

mapping = { 0: "zero", 1: "one", 2: "two", 3: "three", 4: "four", 5: "five", 6: "six", 7: "seven", 8: "eight", 9: "nine", }

In [23]:

say_digit(5321, mapping)

say_digit(5321, mapping)

five
three
two
one

In [1]:

def say_digit_reverse(n, mapping):

    """
    Example of tail recursion
    """
    # 1. Base case
    if n == 0:
        return 0

    # 2. Processing
    # extract digit
    digit = n % 10

    # print the extracted digit right away
    # before going to recursive call
    print(mapping[digit])

    # 3. Recursive relation
    n = say_digit_reverse(n // 10, mapping)

def say_digit_reverse(n, mapping): """ Example of tail recursion """ # 1. Base case if n == 0: return 0 # 2. Processing # extract digit digit = n % 10 # print the extracted digit right away # before going to recursive call print(mapping[digit]) # 3. Recursive relation n = say_digit_reverse(n // 10, mapping)

In [2]:

mapping = {
    0: "zero",
    1: "one",
    2: "two",
    3: "three",
    4: "four",
    5: "five",
    6: "six",
    7: "seven",
    8: "eight",
    9: "nine",
}

say_digit_reverse(5321, mapping)

mapping = { 0: "zero", 1: "one", 2: "two", 3: "three", 4: "four", 5: "five", 6: "six", 7: "seven", 8: "eight", 9: "nine", } say_digit_reverse(5321, mapping)

one
two
three
five
0
None
None
None

In [ ]: