E - Find The Multiple

 1 #include <iostream>
 2 #include <algorithm>
 3 using namespace std;
 4 
 5 int n;
 6 bool ok;
 7 
 8 void dfs(unsigned long long x, int y, int k){
 9     if(ok == true) return ;
10     if(x % y == 0){
11         cout << x << endl;
12         ok = true;
13         return;
14     }
15     if(k == 19) return;
16     dfs(x*10, y, k+1);
17     dfs(x*10+1, y, k+1);
18 }
19 
20 int main(){
21     while(cin >> n){
22         if( n == 0)
23             break;
24         ok = false;
25         dfs(1, n, 0);
26     }
27     return 0;
28 }