题目：

题解：

class Solution {
public:
    int ProductSum(int n)
    {
        int sum = 0;
        while(n)
        {
            int temp = n % 10;
            sum += temp*temp;
            n /= 10;
        }
        return sum;
    }

    bool isHappy(int n) {
        int slow = n,fast = n;
        // 快慢指针，找环的相遇位置
        do
        {
            slow = ProductSum(slow);
            fast = ProductSum(ProductSum(fast));
        }while(slow != fast);
        // 如果相遇时是 1 就是快乐数
        return slow == 1;
    }
};