Write an algorithm to determine if a number n 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.
Return True if n is a happy number, and False if not.
Example:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
public class Solution {
HashSet<int> set = new HashSet<int>();
public bool IsHappy(int n) {
if(set.Contains(n)){
return false;
}
if(n==1){
return true;
}
int num = n;
int sum = 0;
while(num>0){
int lsd = num%10;
sum += lsd*lsd;
num = num/10;
}
set.Add(n);
return IsHappy(sum);
}
}Time Complexity: O(n)
Space Complexity: O(n)
