Python Beginner Algorithms Tutorial

Subtract the Product and Sum of Digits of an Integer (via Leetcode)

  • March 28, 2020
  • Key Terms: functions, loops

Problem setup:

This problem can be found on Leetcode.

Given an integer number n, return the difference between the product of its digits and the sum of its digits.

Test Cases

In [3]:
# assert subtract_product_and_sum(35) == 27
  • Product of digits = 3 * 5 = 35
  • Sum of digits = 3 + 5 = 8
  • Difference = 35 - 8 = 27
In [2]:
# assert subtract_product_and_sum(235) == 20
  • Product of digits = 2 3 5 = 30
  • Sum of digits = 2 + 3 + 5 = 10
  • Difference = 30 - 10 = 20

Pseudocode

In [ ]:
# define function to with argument for num
    # cast num to a string to be able to iterate over its digits
    # assign variable to hold product of digits as 1
    # assign variable to hold sum of digits as 0
    
    # iterate over each digit in string version of number:
        # cast string digit to an integer
        # product of digits = product of digits * integer digit
        # sum of digits = sum of digits * integer digit
    # assign variable difference to be product of digits minus sum of digits
    # return difference

My solution above is the simplest possible solution. I wouldn't dwell on space and time complexity here. There's minimal space used as only 3 variables are created (no data structures). For time complexity, the simplest possible operation is done which is a single iteration over each digit in the input integer.

Code

In [1]:
def subtract_product_and_sum(n)
    str_n = str(n)
    product_of_digits = 1
    sum_of_digits = 0
    for number in str_n:
        int_n = int(number)
        product_of_digits *= int_n
        sum_of_digits += int_n
    diff = product_of_digits - sum_of_digits
    return diff

Verify test cases

In [ ]:
assert subtract_product_and_sum(35) == 27
In [ ]:
assert subtract_product_and_sum(235) == 20