leetcode: (202) Happy Number

【Question】

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

方法一：Happy number容易判断，关键是要确定不是happy number的数，不是的话会一直循环下去，得到的中间值也是循环下去的；
因此，将每次得到的中间结果存起来，如果得到的中间结果与存起来的值有相等的话，就不是happy number

class Solution {
public:
bool isHappy(int n)
{
int result;
vector<int> temp;
while(true)
{
temp.push_back(n);
result=0;
while(n>0)
{
result+=(n%10)*(n%10);
n/=10;
}
if (result==1) return true;
else n=(int)result;
for(int i=0;i<temp.size();i++)
{
if (temp[i]==n) return false;
}
}
}
};

Runtime: 4
ms

方法二：利用hashset，当存入的元素与容器里面的相同时就认为不是happy number

public class Solution {
public boolean isHappy(int n) {
Set<Integer> numberSet = new HashSet<Integer>();
int result;
while (true){
if (numberSet.add(n)==false){
return false;
}
result=0;
while(n>0)
{
result+=(n%10)*(n%10);
n/=10;
}
if (result==1) return true;
else n=result;
}
}
}
Runtime: 284
ms