poj1426 Find The Multiple (DFS)

#include<iostream>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> PII;
const ll mod=998244353;
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
//head
#define MAX 1000
int n;
int flag;
void dfs(int cur,ll sum)
{
    if(cur==19)return ;
    if(flag) return ;
   if(sum%n==0&&sum!=0)
   {
       flag=1;
       cout<<sum<<endl;
       return ;
   }
   else
    dfs(cur+1,sum*10),dfs(cur+1,sum*10+1);
}
int main()
{
      cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);
    while(cin>>n)
    {
        if(n==0)break;
        flag=0;
        dfs(0,1);
    }
    return 0;
}