CODEWITHSUNDEEP
pythonpython-3.x
Kevin Dezwots
Kevin Dezwots

Reputation: 25

Printing the number count with the collatz count: specific question

I have this code I wrote, where I want to find out how many iterations n are needed to reach x[n]=1 for a given input integer, and print that amount. (btw it is the collatz count). The code is:

x0 = int(input('Enter number:'))
while x0 > 1:
    print(x0, end=' ')
    if (x0 % 2):
        x0 = 3*x0 + 1
    else:
        x0 = x0//2

print(1, end=' ')

I want to know how many numbers are in the answer, but with this code I got all the answers. (Enter number:3 gives

3 10 5 16 8 4 2 1

but I want my answer to look like this:

8

I thought putting len() after the print would work, but it didn't. How can I do this?

Upvotes: 1

Views: 713

Answers (1)

Patrick Artner
Patrick Artner

Reputation: 51683

Simply add a counter to your while loop:

x0 = int(input('Enter number:'))
counter = 1    # start at 1 b/c adding 1 after the loop
while x0 > 1:
    # increment so you count how often it loops
    counter += 1
    print(x0, end=' ')
    if (x0 % 2):
        x0 = 3*x0 + 1
    else:
        x0 = x0//2

print(1)  # print the 1 and newline

# and print the count as well
print(counter)

Output: 

Enter number:20
20 10 5 16 8 4 2 1
8

You could also collect all numbers in a list:

nums = []
while x0 > 1:
    nums.append(x0)
    if (x0 % 2):
        x0 = 3*x0 + 1
    else:
        x0 = x0//2

nums.append(1)

print(*nums)       # print the whole list here
print(len(nums))   # and it's length

Trivia: the longest collatz below 1,000,000 is 837799 with 525 steps to 1 && xkcd.com take on Collatz Conjecture - you find other limits at wikipedia

Upvotes: 1

Related Questions