[leetcode] 202. Happy Number

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