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
happy number是把一个数的各个位置的数字的平方相加，直到值为1为止。如果一个数是happy number，那么最终的结果一定会是1，如果不是，这个过程将一直持续下去，并且会重复出现以前曾经出现过的数。例如2。
22 = 4
42 = 16
12 + 62 = 37
32 + 72 = 58
52 + 82 = 89
82 + 92 = 145
12 + 42 + 52 = 42
42 + 22 = 20
22 + 02 = 4
···
所以2不是一个happy number。我们的思路就是记录这个过程中出现过的每一个数，如果某些数字在过程中重复出现，则该数肯定不是happy number。如果最后结果是1，则该数是happy number。代码如下：
1 public class Solution { 2 public boolean isHappy(int n) { 3 List<Integer> list = new ArrayList<>(); 4 while (n != 1) { 5 if (list.contains(n)) { 6 return false; 7 } 8 list.add(n); 9 n = toArrayAndSum(n); 10 } 11 return true; 12 } 13 14 public static int toArrayAndSum(int n) { 15 int sum = 0; 16 while (n > 0) { 17 int x = n % 10; 18 n = n / 10; 19 sum = sum + x * x; 20 } 21 return sum; 22 } 23 }