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
思路：把一个数每一位平方后加和得到一个新的数，然后继续对这个新的数做同样的操作。如果最后能得到一个1，则最原始的数就是一个”Happy Number”。如果在还没达到1的过程中出现循环，则这个数肯定不是。用到C++ 的set。set.count()判断一个数是否在set中，set.insert()，向set 中插入元素。INT_MAX，表示最大整数。
class Solution {
public:
bool isHappy(int n) {
if(n==)
return false;
set<long> s;
while(n<=INT_MAX)
{
if(n==)
return true;
if(s.count(n)>)
return false;
s.insert(n);
n=digitSquare(n);
}
return false;
}
long digitSquare(long num)
{
long r=;
int t=;
while(num)
{
t=num%;
r+=t*t;
num/=;
}
return r;
}
};