Python: Least Common Multiple (LCM) of more than two numbers

Python Basic - 1: Exercise-135 with Solution

Write a Python program that calculates the Least Common Multiple (LCM) of more than two numbers. The numbers should be taken from a given list of positive integers.

From Wikipedia,
In arithmetic and number theory, the least common multiple, lowest common multiple, or smallest common multiple of two integers a and b, usually denoted by lcm(a, b), is the smallest positive integer that is divisible by both a and b. Since division of integers by zero is undefined, this definition has meaning only if a and b are both different from zero. However, some authors define lcm(a,0) as 0 for all a, which is the result of taking the lcm to be the least upper bound in the lattice of divisibility.

Sample Solution-1:

Python Code:

# Import the 'reduce' function from the 'functools' module.
from functools import reduce

# Define a function 'test' that calculates the LCM (Least Common Multiple) of a list of numbers.
def test(nums):
    # Use the 'reduce' function to apply the 'lcm' function cumulatively to the elements of 'nums'.
    return reduce(lambda x, y: lcm(x, y), nums)

# Define a function 'gcd' that calculates the Greatest Common Divisor (GCD) of two numbers.
def gcd(a, b):
    # Use the Euclidean algorithm to find the GCD of 'a' and 'b'.
    while b:
        a, b = b, a % b
    return a

# Define a function 'lcm' that calculates the Least Common Multiple (LCM) of two numbers.
def lcm(a, b):
    # Calculate the LCM using the formula: LCM(a, b) = (a * b) / GCD(a, b).
    return a * b // gcd(a, b)

# Test cases with different lists of positive integers.
nums = [4, 6, 8]
print("Original list elements:")
print(nums)
print("LCM of the numbers of the said array of positive integers: ", test(nums))

nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print("\nOriginal list elements:")
print(nums)
print("LCM of the numbers of the said array of positive integers: ", test(nums))

nums = [48, 72, 108]
print("\nOriginal list elements:")
print(nums)
print("LCM of the numbers of the said array of positive integers: ", test(nums))

Sample Output:

Original list elements:
[4, 6, 8]
LCM of the numbers of the said array of positive integers:  24

Original list elements:
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
LCM of the numbers of the said array of positive integers:  2520

Original list elements:
[48, 72, 108]
LCM of the numbers of the said array of positive integers:  432

Explanation:

Here is a breakdown of the above Python code:

• LCM Function (test function):
• The test function takes a list of positive integers as input and calculates the LCM of the numbers.
• It uses the "reduce()" function to apply the "lcm()" function cumulatively to the elements of the input list.
• GCD and LCM Functions (gcd and lcm functions):
• The "gcd()" function calculates the Greatest Common Divisor (GCD) of two numbers using the Euclidean algorithm.
• The "lcm()" function calculates the Least Common Multiple (LCM) of two numbers using the formula: LCM(a, b) = (a * b) / GCD(a, b).

Flowchart:

Sample Solution-2:

Use functools.reduce(), math.gcd() and lcm(x,y) = x * y / gcd(x,y) over the given list.

Python Code:

# Import the 'reduce' function from the 'functools' module.
from functools import reduce
# Import the 'gcd' function from the 'math' module.
from math import gcd

# Define a function 'lcm' that calculates the Least Common Multiple (LCM) of a list of numbers.
def lcm(numbers):
    # Use the 'reduce' function to apply the lambda function cumulatively to the elements of 'numbers'.
    # The lambda function calculates the LCM using the formula: LCM(a, b) = (a * b) / GCD(a, b).
    return reduce((lambda x, y: int(x * y / gcd(x, y))), numbers)

# Test cases with different lists of positive integers.
print(lcm([4, 6, 8]))
print(lcm([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
print(lcm([48, 72, 108]))

Sample Output:

24
2520
432

Explanation:

Here is a breakdown of the above Python code:

• LCM Function (lcm function):
• The "lcm()" function takes a list of numbers as input and calculates the LCM of the numbers.
• It uses the "reduce()" function to apply the lambda function cumulatively to the elements of the input list.
• The lambda function calculates the LCM using the formula: LCM(a, b) = (a * b) / GCD(a, b).

Flowchart:

Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a Python program to alternate the case of each letter in a given string and the first letter of the said string must be uppercase.
Next: Write a Python program to reverse all the words which have odd length.