202. 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

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

思路：就是暴力解，根据定义将数字拆成个数部分，不断的除10，获取所有单独的数字，然后对其求平方,将所有数字保存到一个set里面，当set有重复表示这个不是一个happy number.

class Solution {public:    bool isHappy(int n) {        set<int> iset;        while(1)        {            vector<int> ivec;            while(n>=10)            {                int num = n % 10;                ivec.push_back(num);                n = n/10;            }            ivec.push_back(n);            int res=0;            for(int i = 0; i < ivec.size(); ++i)            {                res += ivec[i]*ivec[i];            }            n=res;            if(res == 1)            {                break;            }            set<int>::iterator iter;            iter = iset.find(res);            if(iter == iset.end())            {                iset.insert(res);            }else{                return false;            }        }        return true;    }};