牛客9-Happy Number

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
#include<map>
#include<queue>
#include<math.h>
#include<vector>
using namespace std;
#define ll long long
ll a[1000];

int main()
{
  ll n;
  cin>>n;
  ll k = 0;
  if(n == 1)
  {
    cout<<2;
    return 0;
  }
  while(n > 0)
  {
    n-=pow(3,k);
    k++;
    if(n < pow(3,k))break;
  }
  int num = 0;
  while(n > 0)
  {
    a[num] = (n%3);
    n /= 3;
    num++;
  }
  
  for(int i = k-1;i >= 0 ;i--)
  if(a[i] == 0)cout<<2;
  else if(a[i] == 1)cout<<3;
  else cout<<6;
}