[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

题意：

判断一个数是否是happy number，将该数的每一位求平方，然后求和得到新的数字，如果是1那就是happy number。否则一直做下去，直到出现1或者这个求得的和已经出现过了。

思路：

使用一个set保存已经求得的和。

代码如下：

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