题目
Write an algorithm to determine if a number n is happy.
A happy number is a number defined by the following process:
- Starting with any positive integer, replace the number by the sum of the squares of its digits.
- Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
- Those numbers for which this process ends in 1 are happy.
Return true if n is a happy number, and false if not.
Example 1:
Input: n = 19
Output: true
Explanation:
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
Example 2:
Input: n = 2
Output: false
Constraints:
1 <= n <= 231 - 1
思路
无
代码
python版本：
class Solution:
def isHappy(self, n: int) -> bool:
def square_and_sum(n):
return reduce(lambda x, y: x+int(y)**2, str(n), 0)
nums = {}
while n != 1 and n not in nums:
nums[n] = 1
n = square_and_sum(n)
return n == 1
