题解 | #快乐数#

class Solution {
public:
  	int nextStep(int cur)
    {
        int res = 0;
        while(cur)
        {
            res += (cur % 10) * (cur % 10);
            cur /= 10;
        }
        return res;
    }
    //根据鸽巢原理，变换过程一定成环
    //若为快乐数，环中数据全部为1
    //否则不为快乐数
    bool happynum(int n)
    {
        int fast = n, slow = n;
        do
        {
            fast = nextStep(nextStep(fast));
            slow = nextStep(slow);
        } while(fast != slow);
        return fast == 1;    
    }
};