halt_at_number_one

# Computes the Collatz sequence for a given integer [Mu: Python 3]
# Copyright 2022, 2023 Roland Richter

# The Collatz sequence is defined as follows:
# * choose an arbitrary positive integer as the starting number
# * then
#   - if the number is even, divide it by two,
#   - if the number is odd, triple it and add one.
# * repeat the computation until the number 1 is reached
#
# see https://en.wikipedia.org/wiki/Collatz_conjecture

# return True if z is even, False otherwise
def is_even(z):
    return z % 2 == 0   # "==" means comparison: lhs equals rhs?

# compute the next Collatz number, as defined above
def next_collatz(n):
    if is_even(n):
        return n//2   # use integer division!
    else:
        return 3*n+1

inp = input("Enter an integer number: ")

# If the user entered something, try to convert it to a number,
# and do Collatz computations for this starting number.
if inp:
    startnum = int(inp)   # convert string to integer

    num = startnum
    nums = []
    step = 0

    while (num > 1):
        print("Step", step, ":", num)

        # First, keep track of the current number, ...
        nums.append(num)

        # ... then, compute the next step, and the next number.
        # Python allows to assign two (or more) values to two
        # (or more) variables in one line
        step, num = step+1, next_collatz(num)

    # After the loop is finished, print the number one last
    # time, then print an "The End" text.
    print("Step", step, ":", num)
    print("The sequence started with", nums[0], "and ends after", step, "steps")
    print("The largest number was", max(nums))

# ----------------------------------------------------------------------
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# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
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