# 202. Happy Number

### Description

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.

### Constraints

### Approach

### Links

* GeeksforGeeks
* [Leetcode](https://leetcode.com/problems/happy-number/)
* ProgramCreek
* YouTube

### **Examples**

{% tabs %}
{% tab title="Example 1" %}
**Input:** 19

**Output:** true

**Explanation:**

12 + 92 = 82

82 + 22 = 68

62 + 82 = 100

12 + 02 + 02 = 1
{% endtab %}
{% endtabs %}

### **Solutions**

{% tabs %}
{% tab title="Solution 1" %}

```java
/**
 * Time complexity : O(log(N))
 * Space complexity : O(log(N))
 */

class Solution {
    public boolean isHappy(int n) {
        Set<Integer> seen = new HashSet();
        while(n != 1 && !seen.contains(n)) {
            seen.add(n);
            n = getNext(n);
        }
        return n == 1;
    }
    
    private int getNext(int n) {
        int sum = 0;
        while(n > 0) {
            int r = n % 10;
            n /= 10;
            sum += r*r;
        }
        return sum;
    }
}
```

{% endtab %}

{% tab title="Solution 2" %}

```java
/**
 * Time complexity : O(log(N))
 * Space complexity : O(1)
 */
 
 class Solution {

     public int getNext(int n) {
        int totalSum = 0;
        while (n > 0) {
            int d = n % 10;
            n = n / 10;
            totalSum += d * d;
        }
        return totalSum;
    }

    public boolean isHappy(int n) {
        int slowRunner = n;
        int fastRunner = getNext(n);
        while (fastRunner != 1 && slowRunner != fastRunner) {
            slowRunner = getNext(slowRunner);
            fastRunner = getNext(getNext(fastRunner));
        }
        return fastRunner == 1;
    }
}
```

{% endtab %}
{% endtabs %}

### **Follow up**

*