main.cpp

#include <iostream>
#include <cmath>
#include <set>

using namespace std;

auto getDigits = [](int n) -> int { return log10(n) + 1; };
auto getIndexedNumber = [](int n1, int n2) -> int { return (int) (n1 / pow(10, n2)) % 10; };

int reduceToHappy(int number){
  int result = 0;
  for(int i=0; i<getDigits(number); i++){
    int digit = getIndexedNumber(number, i);
    result += pow(digit, 2);
  }
  return result;
}

class Solution{
  public:
    Solution(){};
    

    bool isHappy(int n){
      set<int> store;
      set<int>::iterator it_store;

      int number = reduceToHappy(n);
      while(number != 1){
        number = reduceToHappy(number);
        if(store.find(number) != store.end()){
          return false;
        }
        store.insert(number);
      }
      return true;
    }
};

int main(){
  Solution* obj = new Solution();
  if(obj->isHappy(19)){
      cout << "Number is happy" << endl;
  }else{
      cout << "Number is not happy" << endl;
  }
  
  return 0;
}