leetcode-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

题意清楚。要注意的是可能陷入无限循环中。因此要注意，记录之前出现的数字，一旦发现重复的，就代表陷入死循环，返回false。

时间8ms。

代码：

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