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I have the following code which generates a hailstone sequence of numbers given a user specified positive integer.

n = int(input("Enter a number: "))

seq = [n]

while n > 1:
    n = 3 * n + 1 if n % 2 else n // 2
    seq.append(n)

print(len(seq))
print(seq)

When given the number 15 it produces the following:

Enter a number: 15
18
[15, 46, 23, 70, 35, 106, 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]

When given 27 it produces the following:

Enter a number: 27
112
[27, 82, 41, 124, 62, 31, 94, 47, 142, 71, 214, 107, 322, 161, 484, 242, 121, 364,
 182, 91, 274, 137, 412, 206, 103, 310, 155, 466, 233, 700, 350, 175, 526, 263, 790,
 395, 1186, 593, 1780, 890, 445, 1336, 668, 334, 167, 502, 251, 754, 377, 1132, 566,
 283, 850, 425, 1276, 638, 319, 958, 479, 1438, 719, 2158, 1079, 3238, 1619, 4858, 2429, 
 7288, 3644, 1822, 911, 2734, 1367, 4102, 2051, 6154, 3077, 9232, 4616, 2308, 1154, 577, 
 1732, 866, 433, 1300, 650, 325, 976, 488, 244, 122, 61, 184, 92, 46, 23, 70, 35, 106,
 53, 160, 80, 40, 20, 10, 5, 16, 8, 4, 2, 1]

Is there a way to use list comprehension to generate such lists rather than using a while loop?

I realize the python standard does not support using a while loop in list comprehension.

andand
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1 Answers1

-1

No, It is not possible to use while loop inside list comprehension, however you can use something like this.

def hailstorm(n):
    while n > 1:
        n = 3 * n + 1 if n % 2 else n // 2
        yield n


n = int(input("Enter a number: "))

seq = [i for i in hailstorm(n)]
seq.insert(0, n)
print(len(seq))
print(seq)
Aditya Punetha
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