lab1-kgashok.py

Table of Contents

Lab 1: Compute the gcd of two numbers

[TOC]

Problem statement

Write a Python program to compute the greatest common divisor (gcd) of two positive integers.

Sample Input1: 17, 17
Sample Output1: 17

Sample Input2: 0, 17
Sample Output2: 17

Sample Input3: 12, 17
Sample Output3: 1

Sample Input3: 44, 33
Sample Output3: 11

Solution Key

def gcd(number1, number2):
    while True:
	    if number2 != 0:
	        (number1, number2) = (number2, number1 % number2)
	    else:
		    break
    return number1


def get_twonumbers():
    global a, b
    a = input('Enter number: ')
    b = input('Enter number: ')
    a, b =  int (a), int (b)


# Program starts here
a = None  # initializing variables
b = None
get_twonumbers() # to get values from user
gcdval = gcd(a, b)
print ('The gcd is ', gcdval)

CloudCoder Exercise

http://cloudcoder.kgkite.ac.in/cloudcoder/#exercise?c=80,p=6941

Related material

  • How to find the gcd of two numbers using prime factorization? http://j.mp/gcdPrime

  • Why 1 is the common factor? http://j.mp/gcdOne

Pre-Lab Questions

  1. Show your manual workings for the gcd of 924 and 2562.

  2. What is the practical use of calculating the gcd of two numbers?

  3. If you have written the recursive solution of the Euclid algorithm, then write the iterative solution, and vice versa.

  4. How does the algorithm for the gcd of two numbers work? What is the name for this algorithm? Why is it so special?

  5. Why is the global keyword used in the function get_twonumbers?

  6. Is the function get_twonumbers() fruitful or not fruitful?

  7. Define a function is_valid_year with parameter year. The function must return True if the value of year is between 1900 and 3000 (inclusive). Otherwise, it must return False.

Post-lab Questions

  1. What if a or/and b are negative integers? How will you modify the program to handle this? Clue: Use the abs() function.

Bonus 1

  1. How will find the gcd of three integers?

  2. How do you calculate the number of days in a month?

Related Material

PPT Slides showing the Recursive Calls

http://j.mp/gcdDemo

Recursion vs Iteration

def gcd_r(a, b):
	if b == 0:
		return a
	return gcd_r(b, a % b)

Related Problems

Days per month

def is_valid(mnum):
    return 1 <= mnum <= 12


def is_multiple(n, d):
    return n % d == 0


def is_leap(year):
    """
    Whether a year is a leap year?
    The rules are as follows:
      - multiple of 4 and not of 100 or
      - multiple of 400
    """

    return (is_multiple(year, 4)
            and not is_multiple(year, 100)
            or is_multiple(year, 400))


# Number of days per month (except for February in leap years)
mdays = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]


def monthdays(year, month):
    if not is_valid(month):
        return -1

    ndays = mdays[month] + (month == 2 and is_leap(year))
    return ndays
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