LeetCode *** 202. Happy Number

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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;}
};

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