Happy Number

题目：

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

• 1^2 + 9^2 = 82
• 8^2 + 2^2 = 68
• 6^2 + 8^2 = 100
• 1^2 + 0^2 + 02 = 1

思路： 我没啥思路。。直接上代码。但是在discussion里有些巧妙地解法。待洒家去看看。

    public boolean isHappy(int n) {
        HashSet<Integer> set = new HashSet<Integer>();
        while (!set.contains(n)) {
            set.add(n);
            int sum = 0;
            while (n != 0) {
                sum += (n % 10) * (n % 10);
                n /= 10;
            }
            if (sum == 1) {
                return true;
            }else{
                n = sum;
            }
        }
        return false;
    }