202. Happy Number¶

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# @lc app=leetcode id=202 lang=python3
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# [202] Happy Number
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# https://leetcode.com/problems/happy-number/description/
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# algorithms
# Easy (54.87%)
# Likes:    9544
# Dislikes: 1258
# Total Accepted:    1.3M
# Total Submissions: 2.3M
# Testcase Example:  '19'
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# Write an algorithm to determine if a number n is happy.
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# A happy number is a number defined by the following process:
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# 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.
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# Return true if n is a happy number, and false if not.
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# Example 1:
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# 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
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# Example 2:
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# Input: n = 2
# Output: false
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#
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# Constraints:
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# 1 <= n <= 2^31 - 1
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#
#

# @lc code=start
class Solution:

    def isHappy(self, n: int) -> bool:

        s = set()

        while n not in s:
            s.add(n)
            if n == 1:
                return True
            n = self.fn(n)

        return False

    @staticmethod
    def fn(x: int):
        t = 0
        while x > 0:
            m = x % 10
            t += m*m
            x //= 10
        return t
# @lc code=end