# 202. Happy Number (Easy)

https://leetcode.com/problems/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:
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1
```

## Solutions

``````class Solution {

// TODO, is there any situation of endless loop that is not caused by duplicating outcomes?

public boolean isHappy(int n) {
// corner case: n <= 0
if (n <= 0) {
return false;
}

// The endless loop is caused by the fact that certain number returns back to itself
// number after a serials of computations. So keep track of all the resulting numbers
// and jump out he loop once repeated computations take place.
Set<Integer> visited = new HashSet<>();

int val = n;
while (true) {
if (val == 1) {
return true;
}

if (visited.contains(val)) {
break;
}

int tmp = val;
val = 0;

while (tmp != 0) {
val += Math.pow(tmp % 10, 2);
tmp = tmp / 10;
}
}

return false;
}
}
``````