202. Happy Number

https://leetcode.com/problems/happy-number/

Problem

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.

Example:

Input: 19
Output: true
Explanation: 
12 + 92 = 82
82 + 22 = 68
62 + 82 = 100
12 + 02 + 02 = 1

Solution

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

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