import java.util.HashSet;
import java.util.Set;
class Solution {
public String solution(String my_string) {
Set<Character> set = new HashSet<>();
StringBuilder sb = new StringBuilder();
for(int i = 0; i < my_string.length(); i++) {
char c = my_string.charAt(i);
if(!set.contains(c)) { // Set에 이미 있으면 추가 X
set.add(c);
sb.append(c);
}
}
return sb.toString();
}
}