LeetCode 202.Happy Number

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

LeetCode 202题，循环计算给定整数的各位之和的平方，最后得到1的返回true。Accepted代码如下：

class Solution {
    public boolean isHappy(int n) {
        List<Integer> list = new ArrayList<>();
        int temp = happy(n);
        while (temp != 1 && !list.contains(temp)) {
            list.add(temp);
            temp = happy(temp);
        }
        if (temp == 1) {
            return true;
        }
        return false;
    }
    public int happy(int n) {
        int sum = 0, a = 0;
        while (n > 0) {
            a = n % 10;
            n /= 10;
            sum += a * a;
        }
        return sum;
    }
}

此题走了一些弯路，开始把add放在循环最后，导致每次循环只能走一遍，费了一些时间。