コラッツ予想を1千万まで回してみた

collatz.py

#!/bin/env/python3

def even(x: int) -> int:
    return x // 2

def odd(x: int) -> int:
    return 3 * x + 1

def collatz(memo: set[int], x: int) -> None:
    original = x
    while x != 1:
        if x in memo:
            break
        memo.add(x)
        if x % 2 == 0:
            x = even(x)
        else:
            x = odd(x)
    print(f"{original} meets collatz problem")

def main() -> None:
    memo = set()
    i = 0
    while i < 10_000_000:
        collatz(memo, i)
        i+=1

if __name__ == "__main__":
    main()