[LeetCode] Happy Number _leetcode

少年击剑更吹箫，剑气箫心一例消。这篇文章主要讲述[LeetCode] Happy Number相关的知识，希望能为你提供帮助。
Write an algorithm to determine if a number 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, and 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 numbers.
Example: 19 is a happy number

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

【[LeetCode] Happy Number】快乐数有以下的特性：在给定的进位制下，该数字所有数位(digits)的平方和，得到的新数再次求所有数位的平方和，如此重复进行，最终结果必为1。
非快乐数有以下的特性：所有不快乐数的数位平方和计算，最後都会进入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循环中。
所以外层循环：判断是否为快乐数和非快乐数。内层循环对n进行快乐数分解计算。

class Solution { public: bool isHappy(int n) { while (n != 1 & & n != 4) { int sum = 0, tmp = 0; while (n != 0) { tmp = n % 10; sum += tmp * tmp; n /= 10; } n = sum; } return n == 1; } }; // 3 ms