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202. Happy Number

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:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Example 2:

Input: n = 2
Output: false

 

Constraints:

• 1 <= n <= 231 - 1

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SOL：

參考李根逸博士的影片，已知題目說明會有cycle產生，使用快慢指針的方法來加速走到重覆處，若最後重複的是1則為快樂數。

【C 語言的 LeetCode 30 天挑戰】第二天 (Happy Number)