Happy Number

题目：

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

分析：使用递归求

代码：

class Solution {public:    bool isHappy(int n) {        if(n==1) return true;        if(n<10)        {            if(n==7)return true;            else return false;        }        int sum=0;        while(n>0)        {            sum+=((n%10)*(n%10));            n/=10;                }        if(sum==1)return true;        return isHappy(sum);    }};