202.快乐数 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

• 12 + 92 = 82
• 82 + 22 = 68
• 62 + 82 = 100
• 12 + 02 + 02 = 1

Credits:
Special thanks to @mithmatt and @ts for adding this problem and creating all test cases.

public class Solution {
    public int GetSquareSum(int num)
    {
        int sum = 0;
        while (num >= 1)
        {
            if (num >= 10)
            {
                sum += (num % 10) * (num % 10);
            }
            else
            {
                sum += num * num;
            }
            num = num/10;
        }
        return sum;
    }
    public bool IsHappy(int n)
    {
        List<int> numberList = new List<int>();
        while (true)
        {
            n = GetSquareSum(n);
            if (n == 1)
            {
                return true;
            }
            else if (numberList.IndexOf(n) >= 0)
            {
                return false;
            }
            numberList.Add(n);
        }            
    }
}

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