202. Happy Number
note: can also use the Floyd’s cycle detection algo.
1class Solution:
2 def isHappy(self, n: int) -> bool:
3 seen = set()
4 while n != 1 and n not in seen:
5 seen.add(n)
6 n = sum((int(ch) ** 2) for ch in str(n))
7
8 return n == 1