Functions in Python

Problem Set - Part I

Problem 1: Even numbers

Write a Python function filter_even_numbers that takes a list of numbers and returns a new list containing only the even numbers.

Example Input: [1, 2, 3, 4]
Example Output: [2, 4]

Solution

def filter_even_numbers(numbers):
  even_numbers = [] # create an empty list for the even numbers
  for num in numbers:
    if num % 2 == 0: # if the number is divisable by 2 then it is even
      even_numbers.append (num) # if so, add it to the list of even numbers
  return even_numbers

filter_even_numbers([1, 2, 3, 4])

[2, 4]

Solution #2

def filter_even_numbers_v2(numbers):
  return [num for num in numbers if num % 2 == 0]

filter_even_numbers_v2([1, 2, 3, 4])

[2, 4]

Problem 2: Fizz Buzz

Write a Python function fizzbuzz that takes a number and returns "Fizz" if the number is divisible by 3, "Buzz" if the number is divisible by 5, and "FizzBuzz" if the number is divisible by both 3 and 5. Otherwise, returns the number.

Solution

def fizzbuzz(number):
  if number % 3 == 0 and number % 5 == 0:
    return "FizzBuzz"
  elif number % 3 == 0:
    return "Fizz"
  elif number % 5 == 0:
    return "Buzz"
  else:
    return number

fizzbuzz(15)

'FizzBuzz'

fizzbuzz(5)

'Buzz'

fizzbuzz(3)

'Fizz'

fizzbuzz(1)

Problem 3: Second largest

Write a Python function find_second_largest that takes a list of positive numbers and returns the second largest number in the list without sorting the list.

Example Input: [2, 5, 7, 1, 8, 3, 9]
Example Output: 8

Solution

def find_second_largest(numbers):
  largest = -1
  second_largest = -1
  for num in numbers:
    if num > largest:
      second_largest = largest
      largest = num
    elif num > second_largest:
      second_largest = num
  return second_largest

find_second_largest([2, 5, 7, 1, 8, 3, 9])

Problem 4: Most common letter

Write a Python function find_most_common_letter that takes a string and returns the most common letter in the string.

Example Input: "Hello, World!"
Example Output: 'L'