LeetCode *** 202. 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：

数字	平方
1	1
2	4
3	9
4	16
5	27
6	36
7	49
8	64
9	81

由上图分析可知，根据规则，2，3，5，6，8，9最终都会转换成4，而只有7会转成1。那么只要一个循环之后判断结果是否<10，如果<10了，那么判断该数是否等于1或者等于7即可。

代码：

class Solution {
public:
bool isHappy(int n) {
if(n==0)return false;

int res=n;
while(res>9){
int tmp=res;
res=0;
while(tmp){
res+=(tmp%10)*(tmp%10);
tmp/=10;
}
}

if(res==1||res==7)return true;
else return false;

}
};