> For the complete documentation index, see [llms.txt](https://maksimdan.gitbook.io/interview-practice-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://maksimdan.gitbook.io/interview-practice-problems/leetcode_sessions/202-happy-number.md).

# 202 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

```
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1
```

**The Idea:** Perform the sum of squares operation until either you trace back up, or 1 is reached. **Complexity:** ?

```python
def getSquareDigitSum(self, num):
    """
    :param num: int
    :return: sum of squared digits
    """
    return sum(int(i)**2 for i in str(num))

def isHappy(self, n):
    """
    :param n: int
    :return: bool
    """

    visited = set()
    cur_sum = self.getSquareDigitSum(n)
    if cur_sum == 1:
        return True

    while not visited.__contains__(cur_sum):
        visited.add(cur_sum)
        cur_sum = self.getSquareDigitSum(cur_sum)
        if cur_sum == 1:
            return True

    return False
```


---

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