202. 快乐数

    // 快慢指针
    public boolean isHappy(int n) {
        if (n == 1) {
            return true;
        }
        int slow = n, fast = n;
        do {
            slow = bitSquareSum(slow);
            fast = bitSquareSum(fast);
            fast = bitSquareSum(fast);
        } while (slow != fast);

        return slow == 1;
    }

    private int bitSquareSum(int n) {
        int sum = 0;
        while (n > 0) {
            sum += Math.pow(n % 10, 2);
            n = n / 10;
        }
        return sum;
    }


    // 集合
    public boolean isHappy2(int n) {
        Set<Integer> set = new HashSet<>();
        int m = 0;
        while (true) {
            while (n != 0) {
                m += Math.pow(n % 10, 2);
                n = n / 10;
            }
            if (m == 1) {
                return true;
            }
            if (set.contains(m)) {
                return false;
            } else {
                set.add(m);
                n = m;
                m = 0;
            }
        }
    }