1
class Solution {
2
  public String removeDuplicates(String s) {
3
    Stack<Character> st = new Stack<>();
4
    int i = s.length() - 1;
5
    while (i >= 0) {
6
      char ch = s.charAt(i);
7
      if (st.size() > 0 && ch == st.peek()) {
8
        st.pop();
9
      } else {
10
        st.push(ch);
11
      }
12
      i--;
13
    }
14
    StringBuilder ans = new StringBuilder("");
15
    while (!st.isEmpty()) {
16
      ans.append(st.pop());
17
    }
18
    return ans.toString();
19
  }
20
}