202. Happy Number

题目：Happy Number

原题链接：https://leetcode.com/problems/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: 19 is a happy number
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

编写一个算法判断一个数字是不是“happy”。
判断标准是：将这个数字的各个位上的数字的平方相加，组成新的数字，然后继续取各个位上的平方和，一直到陷入循环，当中结果为1的循环表示“happy”。

例子：对19进行判断：

由于最后陷入的是一个1的死循环，所以这个是一个“happy”数字。

只要模拟上述过程就可以了，模拟过程中每次查询当前组成的数字是不是出现过，如果出现过说明进入了循环，可以退出模拟了，因为1的循环是本身的自循环，所以直接再判断当前组成的数字是不是1就行。

代码如下：

class Solution {public:    bool isHappy(int n) {        vector<int> pre;        int now = n;        process(pre, now);        if (now == 1) return true;        else return false;    }    void process(vector<int>& pre, int& now) {        if(now == 1) return;        for (int i = 0; i < pre.size(); ++i) {            if (now == pre[i]) return;         }        pre.push_back(now);        int sum = 0;        while(now) {            sum += (now % 10) * (now % 10);            now /= 10;        }        now = sum;        process(pre, now);    }};