[leetcode 202] Happy Number

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

 

난이도: 쉬움

문제 풀이:

사이클 발생 여부를 확인한다.

class Solution {
public:
    
    bool isHappy(int n) {
        
        if(n==1) return true;
        
        unordered_map<int, int> um;
        
        while(1){
            int sum = 0;
            while(n > 0){
                int tmp = n % 10;
                sum += tmp * tmp;
                n/=10;
            }
        
            if(sum == 1) return true;
            um[sum]++;
            
            if(um[sum] > 1){
                return false;
            }
            n = sum;
        }
        
     
    }
};