# 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:

``````Input: 19
Output: true
Explanation:
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
``````

## Analysis

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if this set contains no element e2 such that (e==null ? e2==null : e.equals(e2)). If this set already contains the element, the call leaves the set unchanged and returns false.

## Solution

``````class Solution {
public boolean isHappy(int n) {
long t = n;
Set<Long> seen = new HashSet<Long>();
t = process(t);
if (t == 1) {
return true;
}
}
return false;
}

private long process(long n) {
long res = 0;
while (n > 0) {
long rem = n % 10;
res += rem * rem;
n /= 10;
}
return res;
}
}
``````

## Reference

https://leetcode.com/problems/happy-number/discuss/56913/Beat-90-Fast-Easy-Understand-Java-Solution-with-Brief-Explanation