[LeetCode]Happy Number

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

问题在于判断是否进入循环，可以用Hash table记录出现过的数字，当再次出现，则进入循环。和Fraction to Recurring Decimal问题类似。

class Solution {
public:
    bool isHappy(int n) {
        unordered_set<int> showed;
        if(n<1)
        {
            return false;
        }
        if(n==1)
        {
            return true;
        }
        int s;
        while(true)
        {
            s=0;
            while(n!=0)
            {
                s+=(n%10)*(n%10);
                n/=10;
            }
            if(s==1)
            {
                return true;
            }
            else if(showed.find(s)!=showed.end())
            {
                return false;
            }
            showed.insert(s);
            n=s;
        }
    }
};