202. Happy Number

采得百花成蜜后，为谁辛苦为谁甜。这篇文章主要讲述202. 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

题目含义：对任意一个正整数，求每个数位上数字的平方并加和后得出新的正整数，循环此过程若最终收敛为1，则该数字为happy number，否则程序可能从某个数开始陷入循环。

1public boolean isHappy(int n) { 2if (n < 1)return false; 3HashSet< Integer> set = new HashSet< > (32); // 用于保存中间出现的结果 4set.add(1); 5int tmp; 6int newN; 7// n的值不能重复出现，否则会死循环 8while (!set.contains(n)) { 9set.add(n); 10newN = 0; 11while (n > 0) { 12tmp = n % 10; 13n /= 10; 14newN += tmp * tmp; 15} 16n = newN; 17} 18return n == 1; 19}

【202. Happy Number】