# 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:

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

# Solution

Approach 1: Iteration -- use a set to deduplicate, or use Floyd cycle detection algorithm as seen in linked list cycle problem.

# Code (Python)

Approach 1:

class Solution:
    def isHappy(self, n: int) -> bool:
        history = set()
        current = n
        while current != 1 and current not in history:
            history.add(current)
            current = self.calc(current)
        if current == 1:
            return True
        return False
    
    def calc(self, num):
        total = 0
        while num:
            total += (num % 10) ** 2
            num = num // 10
        return total

# Code (C++)

Approach 1:

class Solution {
public:
    bool isHappy(int n) {
        unordered_set<int> visited;
        while (n != 1)
        {
            if (visited.find(n) != visited.end()) return false;
            visited.insert(n);
            int nextNum = 0;
            while (n > 0)
            {
                int tmp = n % 10;
                nextNum += tmp * tmp;
                n = n / 10;
            }
            n = nextNum;
        }
        return true;
    }
};