竟然可以使用"双指针"，类似判断链表中是否有环的思路！妙！
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: *
Input: 19 Output: true *Explanation: *12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
link:{sourcedir}/_0202_HappyNumber.java[role=include]